Cockpit-cpp/ZjQt/ffmpeg5-1-2/include/libavcodec/avcodec.h

/*
 * copyright (c) 2001 Fabrice Bellard
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#ifndef AVCODEC_AVCODEC_H
#define AVCODEC_AVCODEC_H

/**
 * @file
 * @ingroup libavc
 * Libavcodec external API header
 */

#include "libavutil/samplefmt.h"
#include "libavutil/attributes.h"
#include "libavutil/avutil.h"
#include "libavutil/buffer.h"
#include "libavutil/dict.h"
#include "libavutil/frame.h"
#include "libavutil/log.h"
#include "libavutil/pixfmt.h"
#include "libavutil/rational.h"

#include "codec.h"
#include "codec_desc.h"
#include "codec_par.h"
#include "codec_id.h"
#include "defs.h"
#include "packet.h"
#include "version_major.h"
#ifndef HAVE_AV_CONFIG_H
/* When included as part of the ffmpeg build, only include the major version
 * to avoid unnecessary rebuilds. When included externally, keep including
 * the full version information. */
#include "version.h"
#endif

/**
 * @defgroup libavc libavcodec
 * Encoding/Decoding Library
 *
 * @{
 *
 * @defgroup lavc_decoding Decoding
 * @{
 * @}
 *
 * @defgroup lavc_encoding Encoding
 * @{
 * @}
 *
 * @defgroup lavc_codec Codecs
 * @{
 * @defgroup lavc_codec_native Native Codecs
 * @{
 * @}
 * @defgroup lavc_codec_wrappers External library wrappers
 * @{
 * @}
 * @defgroup lavc_codec_hwaccel Hardware Accelerators bridge
 * @{
 * @}
 * @}
 * @defgroup lavc_internal Internal
 * @{
 * @}
 * @}
 */

/**
 * @ingroup libavc
 * @defgroup lavc_encdec send/receive encoding and decoding API overview
 * @{
 *
 * The avcodec_send_packet()/avcodec_receive_frame()/avcodec_send_frame()/
 * avcodec_receive_packet() functions provide an encode/decode API, which
 * decouples input and output.
 *
 * The API is very similar for encoding/decoding and audio/video, and works as
 * follows:
 * - Set up and open the AVCodecContext as usual.
 * - Send valid input:
 *   - For decoding, call avcodec_send_packet() to give the decoder raw
 *     compressed data in an AVPacket.
 *   - For encoding, call avcodec_send_frame() to give the encoder an AVFrame
 *     containing uncompressed audio or video.
 *
 *   In both cases, it is recommended that AVPackets and AVFrames are
 *   refcounted, or libavcodec might have to copy the input data. (libavformat
 *   always returns refcounted AVPackets, and av_frame_get_buffer() allocates
 *   refcounted AVFrames.)
 * - Receive output in a loop. Periodically call one of the avcodec_receive_*()
 *   functions and process their output:
 *   - For decoding, call avcodec_receive_frame(). On success, it will return
 *     an AVFrame containing uncompressed audio or video data.
 *   - For encoding, call avcodec_receive_packet(). On success, it will return
 *     an AVPacket with a compressed frame.
 *
 *   Repeat this call until it returns AVERROR(EAGAIN) or an error. The
 *   AVERROR(EAGAIN) return value means that new input data is required to
 *   return new output. In this case, continue with sending input. For each
 *   input frame/packet, the codec will typically return 1 output frame/packet,
 *   but it can also be 0 or more than 1.
 *
 * At the beginning of decoding or encoding, the codec might accept multiple
 * input frames/packets without returning a frame, until its internal buffers
 * are filled. This situation is handled transparently if you follow the steps
 * outlined above.
 *
 * In theory, sending input can result in EAGAIN - this should happen only if
 * not all output was received. You can use this to structure alternative decode
 * or encode loops other than the one suggested above. For example, you could
 * try sending new input on each iteration, and try to receive output if that
 * returns EAGAIN.
 *
 * End of stream situations. These require "flushing" (aka draining) the codec,
 * as the codec might buffer multiple frames or packets internally for
 * performance or out of necessity (consider B-frames).
 * This is handled as follows:
 * - Instead of valid input, send NULL to the avcodec_send_packet() (decoding)
 *   or avcodec_send_frame() (encoding) functions. This will enter draining
 *   mode.
 * - Call avcodec_receive_frame() (decoding) or avcodec_receive_packet()
 *   (encoding) in a loop until AVERROR_EOF is returned. The functions will
 *   not return AVERROR(EAGAIN), unless you forgot to enter draining mode.
 * - Before decoding can be resumed again, the codec has to be reset with
 *   avcodec_flush_buffers().
 *
 * Using the API as outlined above is highly recommended. But it is also
 * possible to call functions outside of this rigid schema. For example, you can
 * call avcodec_send_packet() repeatedly without calling
 * avcodec_receive_frame(). In this case, avcodec_send_packet() will succeed
 * until the codec's internal buffer has been filled up (which is typically of
 * size 1 per output frame, after initial input), and then reject input with
 * AVERROR(EAGAIN). Once it starts rejecting input, you have no choice but to
 * read at least some output.
 *
 * Not all codecs will follow a rigid and predictable dataflow; the only
 * guarantee is that an AVERROR(EAGAIN) return value on a send/receive call on
 * one end implies that a receive/send call on the other end will succeed, or
 * at least will not fail with AVERROR(EAGAIN). In general, no codec will
 * permit unlimited buffering of input or output.
 *
 * A codec is not allowed to return AVERROR(EAGAIN) for both sending and receiving. This
 * would be an invalid state, which could put the codec user into an endless
 * loop. The API has no concept of time either: it cannot happen that trying to
 * do avcodec_send_packet() results in AVERROR(EAGAIN), but a repeated call 1 second
 * later accepts the packet (with no other receive/flush API calls involved).
 * The API is a strict state machine, and the passage of time is not supposed
 * to influence it. Some timing-dependent behavior might still be deemed
 * acceptable in certain cases. But it must never result in both send/receive
 * returning EAGAIN at the same time at any point. It must also absolutely be
 * avoided that the current state is "unstable" and can "flip-flop" between
 * the send/receive APIs allowing progress. For example, it's not allowed that
 * the codec randomly decides that it actually wants to consume a packet now
 * instead of returning a frame, after it just returned AVERROR(EAGAIN) on an
 * avcodec_send_packet() call.
 * @}
 */

/**
 * @defgroup lavc_core Core functions/structures.
 * @ingroup libavc
 *
 * Basic definitions, functions for querying libavcodec capabilities,
 * allocating core structures, etc.
 * @{
 */

/**
 * @ingroup lavc_encoding
 * minimum encoding buffer size
 * Used to avoid some checks during header writing.
 */
#define AV_INPUT_BUFFER_MIN_SIZE 16384

/**
 * @ingroup lavc_encoding
 */
typedef struct RcOverride{
    int start_frame;
    int end_frame;
    int qscale; // If this is 0 then quality_factor will be used instead.
    float quality_factor;
} RcOverride;

/* encoding support
   These flags can be passed in AVCodecContext.flags before initialization.
   Note: Not everything is supported yet.
*/

/**
 * Allow decoders to produce frames with data planes that are not aligned
 * to CPU requirements (e.g. due to cropping).
 */
#define AV_CODEC_FLAG_UNALIGNED       (1 <<  0)
/**
 * Use fixed qscale.
 */
#define AV_CODEC_FLAG_QSCALE          (1 <<  1)
/**
 * 4 MV per MB allowed / advanced prediction for H.263.
 */
#define AV_CODEC_FLAG_4MV             (1 <<  2)
/**
 * Output even those frames that might be corrupted.
 */
#define AV_CODEC_FLAG_OUTPUT_CORRUPT  (1 <<  3)
/**
 * Use qpel MC.
 */
#define AV_CODEC_FLAG_QPEL            (1 <<  4)
/**
 * Don't output frames whose parameters differ from first
 * decoded frame in stream.
 */
#define AV_CODEC_FLAG_DROPCHANGED     (1 <<  5)
/**
 * Use internal 2pass ratecontrol in first pass mode.
 */
#define AV_CODEC_FLAG_PASS1           (1 <<  9)
/**
 * Use internal 2pass ratecontrol in second pass mode.
 */
#define AV_CODEC_FLAG_PASS2           (1 << 10)
/**
 * loop filter.
 */
#define AV_CODEC_FLAG_LOOP_FILTER     (1 << 11)
/**
 * Only decode/encode grayscale.
 */
#define AV_CODEC_FLAG_GRAY            (1 << 13)
/**
 * error[?] variables will be set during encoding.
 */
#define AV_CODEC_FLAG_PSNR            (1 << 15)
#if FF_API_FLAG_TRUNCATED
/**
 * Input bitstream might be truncated at a random location
 * instead of only at frame boundaries.
 *
 * @deprecated use codec parsers for packetizing input
 */
#define AV_CODEC_FLAG_TRUNCATED       (1 << 16)
#endif
/**
 * Use interlaced DCT.
 */
#define AV_CODEC_FLAG_INTERLACED_DCT  (1 << 18)
/**
 * Force low delay.
 */
#define AV_CODEC_FLAG_LOW_DELAY       (1 << 19)
/**
 * Place global headers in extradata instead of every keyframe.
 */
#define AV_CODEC_FLAG_GLOBAL_HEADER   (1 << 22)
/**
 * Use only bitexact stuff (except (I)DCT).
 */
#define AV_CODEC_FLAG_BITEXACT        (1 << 23)
/* Fx : Flag for H.263+ extra options */
/**
 * H.263 advanced intra coding / MPEG-4 AC prediction
 */
#define AV_CODEC_FLAG_AC_PRED         (1 << 24)
/**
 * interlaced motion estimation
 */
#define AV_CODEC_FLAG_INTERLACED_ME   (1 << 29)
#define AV_CODEC_FLAG_CLOSED_GOP      (1U << 31)

/**
 * Allow non spec compliant speedup tricks.
 */
#define AV_CODEC_FLAG2_FAST           (1 <<  0)
/**
 * Skip bitstream encoding.
 */
#define AV_CODEC_FLAG2_NO_OUTPUT      (1 <<  2)
/**
 * Place global headers at every keyframe instead of in extradata.
 */
#define AV_CODEC_FLAG2_LOCAL_HEADER   (1 <<  3)

/**
 * timecode is in drop frame format. DEPRECATED!!!!
 */
#define AV_CODEC_FLAG2_DROP_FRAME_TIMECODE (1 << 13)

/**
 * Input bitstream might be truncated at a packet boundaries
 * instead of only at frame boundaries.
 */
#define AV_CODEC_FLAG2_CHUNKS         (1 << 15)
/**
 * Discard cropping information from SPS.
 */
#define AV_CODEC_FLAG2_IGNORE_CROP    (1 << 16)

/**
 * Show all frames before the first keyframe
 */
#define AV_CODEC_FLAG2_SHOW_ALL       (1 << 22)
/**
 * Export motion vectors through frame side data
 */
#define AV_CODEC_FLAG2_EXPORT_MVS     (1 << 28)
/**
 * Do not skip samples and export skip information as frame side data
 */
#define AV_CODEC_FLAG2_SKIP_MANUAL    (1 << 29)
/**
 * Do not reset ASS ReadOrder field on flush (subtitles decoding)
 */
#define AV_CODEC_FLAG2_RO_FLUSH_NOOP  (1 << 30)

/* Unsupported options :
 *              Syntax Arithmetic coding (SAC)
 *              Reference Picture Selection
 *              Independent Segment Decoding */
/* /Fx */
/* codec capabilities */

/* Exported side data.
   These flags can be passed in AVCodecContext.export_side_data before initialization.
*/
/**
 * Export motion vectors through frame side data
 */
#define AV_CODEC_EXPORT_DATA_MVS         (1 << 0)
/**
 * Export encoder Producer Reference Time through packet side data
 */
#define AV_CODEC_EXPORT_DATA_PRFT        (1 << 1)
/**
 * Decoding only.
 * Export the AVVideoEncParams structure through frame side data.
 */
#define AV_CODEC_EXPORT_DATA_VIDEO_ENC_PARAMS (1 << 2)
/**
 * Decoding only.
 * Do not apply film grain, export it instead.
 */
#define AV_CODEC_EXPORT_DATA_FILM_GRAIN (1 << 3)

/**
 * The decoder will keep a reference to the frame and may reuse it later.
 */
#define AV_GET_BUFFER_FLAG_REF (1 << 0)

/**
 * The encoder will keep a reference to the packet and may reuse it later.
 */
#define AV_GET_ENCODE_BUFFER_FLAG_REF (1 << 0)

struct AVCodecInternal;

/**
 * main external API structure.
 * New fields can be added to the end with minor version bumps.
 * Removal, reordering and changes to existing fields require a major
 * version bump.
 * You can use AVOptions (av_opt* / av_set/get*()) to access these fields from user
 * applications.
 * The name string for AVOptions options matches the associated command line
 * parameter name and can be found in libavcodec/options_table.h
 * The AVOption/command line parameter names differ in some cases from the C
 * structure field names for historic reasons or brevity.
 * sizeof(AVCodecContext) must not be used outside libav*.
 */
typedef struct AVCodecContext {
    /**
     * information on struct for av_log
     * - set by avcodec_alloc_context3
     */
    const AVClass *av_class;
    int log_level_offset;

    enum AVMediaType codec_type; /* see AVMEDIA_TYPE_xxx */
    const struct AVCodec  *codec;
    enum AVCodecID     codec_id; /* see AV_CODEC_ID_xxx */

    /**
     * fourcc (LSB first, so "ABCD" -> ('D'<<24) + ('C'<<16) + ('B'<<8) + 'A').
     * This is used to work around some encoder bugs.
     * A demuxer should set this to what is stored in the field used to identify the codec.
     * If there are multiple such fields in a container then the demuxer should choose the one
     * which maximizes the information about the used codec.
     * If the codec tag field in a container is larger than 32 bits then the demuxer should
     * remap the longer ID to 32 bits with a table or other structure. Alternatively a new
     * extra_codec_tag + size could be added but for this a clear advantage must be demonstrated
     * first.
     * - encoding: Set by user, if not then the default based on codec_id will be used.
     * - decoding: Set by user, will be converted to uppercase by libavcodec during init.
     */
    unsigned int codec_tag;

    void *priv_data;

    /**
     * Private context used for internal data.
     *
     * Unlike priv_data, this is not codec-specific. It is used in general
     * libavcodec functions.
     */
    struct AVCodecInternal *internal;

    /**
     * Private data of the user, can be used to carry app specific stuff.
     * - encoding: Set by user.
     * - decoding: Set by user.
     */
    void *opaque;

    /**
     * the average bitrate
     * - encoding: Set by user; unused for constant quantizer encoding.
     * - decoding: Set by user, may be overwritten by libavcodec
     *             if this info is available in the stream
     */
    int64_t bit_rate;

    /**
     * number of bits the bitstream is allowed to diverge from the reference.
     *           the reference can be CBR (for CBR pass1) or VBR (for pass2)
     * - encoding: Set by user; unused for constant quantizer encoding.
     * - decoding: unused
     */
    int bit_rate_tolerance;

    /**
     * Global quality for codecs which cannot change it per frame.
     * This should be proportional to MPEG-1/2/4 qscale.
     * - encoding: Set by user.
     * - decoding: unused
     */
    int global_quality;

    /**
     * - encoding: Set by user.
     * - decoding: unused
     */
    int compression_level;
#define FF_COMPRESSION_DEFAULT -1

    /**
     * AV_CODEC_FLAG_*.
     * - encoding: Set by user.
     * - decoding: Set by user.
     */
    int flags;

    /**
     * AV_CODEC_FLAG2_*
     * - encoding: Set by user.
     * - decoding: Set by user.
     */
    int flags2;

    /**
     * some codecs need / can use extradata like Huffman tables.
     * MJPEG: Huffman tables
     * rv10: additional flags
     * MPEG-4: global headers (they can be in the bitstream or here)
     * The allocated memory should be AV_INPUT_BUFFER_PADDING_SIZE bytes larger
     * than extradata_size to avoid problems if it is read with the bitstream reader.
     * The bytewise contents of extradata must not depend on the architecture or CPU endianness.
     * Must be allocated with the av_malloc() family of functions.
     * - encoding: Set/allocated/freed by libavcodec.
     * - decoding: Set/allocated/freed by user.
     */
    uint8_t *extradata;
    int extradata_size;

    /**
     * This is the fundamental unit of time (in seconds) in terms
     * of which frame timestamps are represented. For fixed-fps content,
     * timebase should be 1/framerate and timestamp increments should be
     * identically 1.
     * This often, but not always is the inverse of the frame rate or field rate
     * for video. 1/time_base is not the average frame rate if the frame rate is not
     * constant.
     *
     * Like containers, elementary streams also can store timestamps, 1/time_base
     * is the unit in which these timestamps are specified.
     * As example of such codec time base see ISO/IEC 14496-2:2001(E)
     * vop_time_increment_resolution and fixed_vop_rate
     * (fixed_vop_rate == 0 implies that it is different from the framerate)
     *
     * - encoding: MUST be set by user.
     * - decoding: the use of this field for decoding is deprecated.
     *             Use framerate instead.
     */
    AVRational time_base;

    /**
     * For some codecs, the time base is closer to the field rate than the frame rate.
     * Most notably, H.264 and MPEG-2 specify time_base as half of frame duration
     * if no telecine is used ...
     *
     * Set to time_base ticks per frame. Default 1, e.g., H.264/MPEG-2 set it to 2.
     */
    int ticks_per_frame;

    /**
     * Codec delay.
     *
     * Encoding: Number of frames delay there will be from the encoder input to
     *           the decoder output. (we assume the decoder matches the spec)
     * Decoding: Number of frames delay in addition to what a standard decoder
     *           as specified in the spec would produce.
     *
     * Video:
     *   Number of frames the decoded output will be delayed relative to the
     *   encoded input.
     *
     * Audio:
     *   For encoding, this field is unused (see initial_padding).
     *
     *   For decoding, this is the number of samples the decoder needs to
     *   output before the decoder's output is valid. When seeking, you should
     *   start decoding this many samples prior to your desired seek point.
     *
     * - encoding: Set by libavcodec.
     * - decoding: Set by libavcodec.
     */
    int delay;


    /* video only */
    /**
     * picture width / height.
     *
     * @note Those fields may not match the values of the last
     * AVFrame output by avcodec_receive_frame() due frame
     * reordering.
     *
     * - encoding: MUST be set by user.
     * - decoding: May be set by the user before opening the decoder if known e.g.
     *             from the container. Some decoders will require the dimensions
     *             to be set by the caller. During decoding, the decoder may
     *             overwrite those values as required while parsing the data.
     */
    int width, height;

    /**
     * Bitstream width / height, may be different from width/height e.g. when
     * the decoded frame is cropped before being output or lowres is enabled.
     *
     * @note Those field may not match the value of the last
     * AVFrame output by avcodec_receive_frame() due frame
     * reordering.
     *
     * - encoding: unused
     * - decoding: May be set by the user before opening the decoder if known
     *             e.g. from the container. During decoding, the decoder may
     *             overwrite those values as required while parsing the data.
     */
    int coded_width, coded_height;

    /**
     * the number of pictures in a group of pictures, or 0 for intra_only
     * - encoding: Set by user.
     * - decoding: unused
     */
    int gop_size;

    /**
     * 像素格式，请参阅AV_PIX_FMT_xxx。
     * 如果从标题中知道，可以由解复用器设置。
     * 如果解码器更清楚，可能会被其覆盖。
     *
     * @note 由于帧重新排序，此字段可能与avcodec_receive_frame（）上次输出的AVFrame值不匹配。
     *
     * - encoding: Set by user.
     * - decoding: Set by user if known, overridden by libavcodec while
     *             parsing the data.
     */
    enum AVPixelFormat pix_fmt;

    /**
     * If non NULL, 'draw_horiz_band' is called by the libavcodec
     * decoder to draw a horizontal band. It improves cache usage. Not
     * all codecs can do that. You must check the codec capabilities
     * beforehand.
     * When multithreading is used, it may be called from multiple threads
     * at the same time; threads might draw different parts of the same AVFrame,
     * or multiple AVFrames, and there is no guarantee that slices will be drawn
     * in order.
     * The function is also used by hardware acceleration APIs.
     * It is called at least once during frame decoding to pass
     * the data needed for hardware render.
     * In that mode instead of pixel data, AVFrame points to
     * a structure specific to the acceleration API. The application
     * reads the structure and can change some fields to indicate progress
     * or mark state.
     * - encoding: unused
     * - decoding: Set by user.
     * @param height the height of the slice
     * @param y the y position of the slice
     * @param type 1->top field, 2->bottom field, 3->frame
     * @param offset offset into the AVFrame.data from which the slice should be read
     */
    void (*draw_horiz_band)(struct AVCodecContext *s,
                            const AVFrame *src, int offset[AV_NUM_DATA_POINTERS],
                            int y, int type, int height);

    /**
     * 回调以选择像素格式。仅解码，可由调用者在avcodec_open2（）之前设置。
     *
     * 由一些解码器调用，以选择将用于输出帧的像素格式。
     * 这主要用于设置硬件加速，然后提供的格式列表包含相应的hwaccel像素格式以及“software”格式。也可以从\ref sw_pix_fmt检索软件像素格式。
     *
     * 当编码帧属性（如分辨率、像素格式等）更改，并且这些新属性支持多个输出格式时，将调用此回调。
     * 如果选择了硬件像素格式，但初始化失败，可能会立即再次调用回调。
     *
     * This callback may be called from different threads if the decoder is
     * multi-threaded, but not from more than one thread simultaneously.
     *
     * @param fmt list of formats which may be used in the current
     *            configuration, terminated by AV_PIX_FMT_NONE.
     * @warning Behavior is undefined if the callback returns a value other
     *          than one of the formats in fmt or AV_PIX_FMT_NONE.
     * @return the chosen format or AV_PIX_FMT_NONE
     */
    enum AVPixelFormat (*get_format)(struct AVCodecContext *s, const enum AVPixelFormat * fmt);

    /**
     * 非B帧之间的最大B帧数
     *注意：相对于输入，输出将延迟max_b_frames+1。
     * - encoding: Set by user.
     * - decoding: unused
     */
    int max_b_frames;

    /**
     * qscale factor between IP and B-frames
     * If > 0 then the last P-frame quantizer will be used (q= lastp_q*factor+offset).
     * If < 0 then normal ratecontrol will be done (q= -normal_q*factor+offset).
     * - encoding: Set by user.
     * - decoding: unused
     */
    float b_quant_factor;

    /**
     * qscale offset between IP and B-frames
     * - encoding: Set by user.
     * - decoding: unused
     */
    float b_quant_offset;

    /**
     * Size of the frame reordering buffer in the decoder.
     * For MPEG-2 it is 1 IPB or 0 low delay IP.
     * - encoding: Set by libavcodec.
     * - decoding: Set by libavcodec.
     */
    int has_b_frames;

    /**
     * qscale factor between P- and I-frames
     * If > 0 then the last P-frame quantizer will be used (q = lastp_q * factor + offset).
     * If < 0 then normal ratecontrol will be done (q= -normal_q*factor+offset).
     * - encoding: Set by user.
     * - decoding: unused
     */
    float i_quant_factor;

    /**
     * qscale offset between P and I-frames
     * - encoding: Set by user.
     * - decoding: unused
     */
    float i_quant_offset;

    /**
     * luminance masking (0-> disabled)
     * - encoding: Set by user.
     * - decoding: unused
     */
    float lumi_masking;

    /**
     * temporary complexity masking (0-> disabled)
     * - encoding: Set by user.
     * - decoding: unused
     */
    float temporal_cplx_masking;

    /**
     * spatial complexity masking (0-> disabled)
     * - encoding: Set by user.
     * - decoding: unused
     */
    float spatial_cplx_masking;

    /**
     * p block masking (0-> disabled)
     * - encoding: Set by user.
     * - decoding: unused
     */
    float p_masking;

    /**
     * darkness masking (0-> disabled)
     * - encoding: Set by user.
     * - decoding: unused
     */
    float dark_masking;

    /**
     * slice count
     * - encoding: Set by libavcodec.
     * - decoding: Set by user (or 0).
     */
    int slice_count;

    /**
     * slice offsets in the frame in bytes
     * - encoding: Set/allocated by libavcodec.
     * - decoding: Set/allocated by user (or NULL).
     */
    int *slice_offset;

    /**
     * sample aspect ratio (0 if unknown)
     * That is the width of a pixel divided by the height of the pixel.
     * Numerator and denominator must be relatively prime and smaller than 256 for some video standards.
     * - encoding: Set by user.
     * - decoding: Set by libavcodec.
     */
    AVRational sample_aspect_ratio;

    /**
     * motion estimation comparison function
     * - encoding: Set by user.
     * - decoding: unused
     */
    int me_cmp;
    /**
     * subpixel motion estimation comparison function
     * - encoding: Set by user.
     * - decoding: unused
     */
    int me_sub_cmp;
    /**
     * macroblock comparison function (not supported yet)
     * - encoding: Set by user.
     * - decoding: unused
     */
    int mb_cmp;
    /**
     * interlaced DCT comparison function
     * - encoding: Set by user.
     * - decoding: unused
     */
    int ildct_cmp;
#define FF_CMP_SAD          0
#define FF_CMP_SSE          1
#define FF_CMP_SATD         2
#define FF_CMP_DCT          3
#define FF_CMP_PSNR         4
#define FF_CMP_BIT          5
#define FF_CMP_RD           6
#define FF_CMP_ZERO         7
#define FF_CMP_VSAD         8
#define FF_CMP_VSSE         9
#define FF_CMP_NSSE         10
#define FF_CMP_W53          11
#define FF_CMP_W97          12
#define FF_CMP_DCTMAX       13
#define FF_CMP_DCT264       14
#define FF_CMP_MEDIAN_SAD   15
#define FF_CMP_CHROMA       256

    /**
     * ME diamond size & shape
     * - encoding: Set by user.
     * - decoding: unused
     */
    int dia_size;

    /**
     * amount of previous MV predictors (2a+1 x 2a+1 square)
     * - encoding: Set by user.
     * - decoding: unused
     */
    int last_predictor_count;

    /**
     * motion estimation prepass comparison function
     * - encoding: Set by user.
     * - decoding: unused
     */
    int me_pre_cmp;

    /**
     * ME prepass diamond size & shape
     * - encoding: Set by user.
     * - decoding: unused
     */
    int pre_dia_size;

    /**
     * subpel ME quality
     * - encoding: Set by user.
     * - decoding: unused
     */
    int me_subpel_quality;

    /**
     * maximum motion estimation search range in subpel units
     * If 0 then no limit.
     *
     * - encoding: Set by user.
     * - decoding: unused
     */
    int me_range;

    /**
     * slice flags
     * - encoding: unused
     * - decoding: Set by user.
     */
    int slice_flags;
#define SLICE_FLAG_CODED_ORDER    0x0001 ///< draw_horiz_band() is called in coded order instead of display
#define SLICE_FLAG_ALLOW_FIELD    0x0002 ///< allow draw_horiz_band() with field slices (MPEG-2 field pics)
#define SLICE_FLAG_ALLOW_PLANE    0x0004 ///< allow draw_horiz_band() with 1 component at a time (SVQ1)

    /**
     * macroblock decision mode
     * - encoding: Set by user.
     * - decoding: unused
     */
    int mb_decision;
#define FF_MB_DECISION_SIMPLE 0        ///< uses mb_cmp
#define FF_MB_DECISION_BITS   1        ///< chooses the one which needs the fewest bits
#define FF_MB_DECISION_RD     2        ///< rate distortion

    /**
     * custom intra quantization matrix
     * Must be allocated with the av_malloc() family of functions, and will be freed in
     * avcodec_free_context().
     * - encoding: Set/allocated by user, freed by libavcodec. Can be NULL.
     * - decoding: Set/allocated/freed by libavcodec.
     */
    uint16_t *intra_matrix;

    /**
     * custom inter quantization matrix
     * Must be allocated with the av_malloc() family of functions, and will be freed in
     * avcodec_free_context().
     * - encoding: Set/allocated by user, freed by libavcodec. Can be NULL.
     * - decoding: Set/allocated/freed by libavcodec.
     */
    uint16_t *inter_matrix;

    /**
     * precision of the intra DC coefficient - 8
     * - encoding: Set by user.
     * - decoding: Set by libavcodec
     */
    int intra_dc_precision;

    /**
     * Number of macroblock rows at the top which are skipped.
     * - encoding: unused
     * - decoding: Set by user.
     */
    int skip_top;

    /**
     * Number of macroblock rows at the bottom which are skipped.
     * - encoding: unused
     * - decoding: Set by user.
     */
    int skip_bottom;

    /**
     * minimum MB Lagrange multiplier
     * - encoding: Set by user.
     * - decoding: unused
     */
    int mb_lmin;

    /**
     * maximum MB Lagrange multiplier
     * - encoding: Set by user.
     * - decoding: unused
     */
    int mb_lmax;

    /**
     * - encoding: Set by user.
     * - decoding: unused
     */
    int bidir_refine;

    /**
     * minimum GOP size
     * - encoding: Set by user.
     * - decoding: unused
     */
    int keyint_min;

    /**
     * number of reference frames
     * - encoding: Set by user.
     * - decoding: Set by lavc.
     */
    int refs;

    /**
     * Note: Value depends upon the compare function used for fullpel ME.
     * - encoding: Set by user.
     * - decoding: unused
     */
    int mv0_threshold;

    /**
     * Chromaticity coordinates of the source primaries.
     * - encoding: Set by user
     * - decoding: Set by libavcodec
     */
    enum AVColorPrimaries color_primaries;

    /**
     * Color Transfer Characteristic.
     * - encoding: Set by user
     * - decoding: Set by libavcodec
     */
    enum AVColorTransferCharacteristic color_trc;

    /**
     * YUV colorspace type.
     * - encoding: Set by user
     * - decoding: Set by libavcodec
     */
    enum AVColorSpace colorspace;

    /**
     * MPEG vs JPEG YUV range.
     * - encoding: Set by user
     * - decoding: Set by libavcodec
     */
    enum AVColorRange color_range;

    /**
     * This defines the location of chroma samples.
     * - encoding: Set by user
     * - decoding: Set by libavcodec
     */
    enum AVChromaLocation chroma_sample_location;

    /**
     * Number of slices.
     * Indicates number of picture subdivisions. Used for parallelized
     * decoding.
     * - encoding: Set by user
     * - decoding: unused
     */
    int slices;

    /** Field order
     * - encoding: set by libavcodec
     * - decoding: Set by user.
     */
    enum AVFieldOrder field_order;

    /* audio only */
    int sample_rate; ///< samples per second

#if FF_API_OLD_CHANNEL_LAYOUT
    /**
     * number of audio channels
     * @deprecated use ch_layout.nb_channels
     */
    attribute_deprecated
    int channels;
#endif

    /**
     * audio sample format
     * - encoding: Set by user.
     * - decoding: Set by libavcodec.
     */
    enum AVSampleFormat sample_fmt;  ///< sample format

    /* The following data should not be initialized. */
    /**
     * Number of samples per channel in an audio frame.
     *
     * - encoding: set by libavcodec in avcodec_open2(). Each submitted frame
     *   except the last must contain exactly frame_size samples per channel.
     *   May be 0 when the codec has AV_CODEC_CAP_VARIABLE_FRAME_SIZE set, then the
     *   frame size is not restricted.
     * - decoding: may be set by some decoders to indicate constant frame size
     */
    int frame_size;

    /**
     * Frame counter, set by libavcodec.
     *
     * - decoding: total number of frames returned from the decoder so far.
     * - encoding: total number of frames passed to the encoder so far.
     *
     *   @note the counter is not incremented if encoding/decoding resulted in
     *   an error.
     */
    int frame_number;

    /**
     * number of bytes per packet if constant and known or 0
     * Used by some WAV based audio codecs.
     */
    int block_align;

    /**
     * Audio cutoff bandwidth (0 means "automatic")
     * - encoding: Set by user.
     * - decoding: unused
     */
    int cutoff;

#if FF_API_OLD_CHANNEL_LAYOUT
    /**
     * Audio channel layout.
     * - encoding: set by user.
     * - decoding: set by user, may be overwritten by libavcodec.
     * @deprecated use ch_layout
     */
    attribute_deprecated
    uint64_t channel_layout;

    /**
     * Request decoder to use this channel layout if it can (0 for default)
     * - encoding: unused
     * - decoding: Set by user.
     * @deprecated use "downmix" codec private option
     */
    attribute_deprecated
    uint64_t request_channel_layout;
#endif

    /**
     * Type of service that the audio stream conveys.
     * - encoding: Set by user.
     * - decoding: Set by libavcodec.
     */
    enum AVAudioServiceType audio_service_type;

    /**
     * desired sample format
     * - encoding: Not used.
     * - decoding: Set by user.
     * Decoder will decode to this format if it can.
     */
    enum AVSampleFormat request_sample_fmt;

    /**
     * This callback is called at the beginning of each frame to get data
     * buffer(s) for it. There may be one contiguous buffer for all the data or
     * there may be a buffer per each data plane or anything in between. What
     * this means is, you may set however many entries in buf[] you feel necessary.
     * Each buffer must be reference-counted using the AVBuffer API (see description
     * of buf[] below).
     *
     * The following fields will be set in the frame before this callback is
     * called:
     * - format
     * - width, height (video only)
     * - sample_rate, channel_layout, nb_samples (audio only)
     * Their values may differ from the corresponding values in
     * AVCodecContext. This callback must use the frame values, not the codec
     * context values, to calculate the required buffer size.
     *
     * This callback must fill the following fields in the frame:
     * - data[]
     * - linesize[]
     * - extended_data:
     *   * if the data is planar audio with more than 8 channels, then this
     *     callback must allocate and fill extended_data to contain all pointers
     *     to all data planes. data[] must hold as many pointers as it can.
     *     extended_data must be allocated with av_malloc() and will be freed in
     *     av_frame_unref().
     *   * otherwise extended_data must point to data
     * - buf[] must contain one or more pointers to AVBufferRef structures. Each of
     *   the frame's data and extended_data pointers must be contained in these. That
     *   is, one AVBufferRef for each allocated chunk of memory, not necessarily one
     *   AVBufferRef per data[] entry. See: av_buffer_create(), av_buffer_alloc(),
     *   and av_buffer_ref().
     * - extended_buf and nb_extended_buf must be allocated with av_malloc() by
     *   this callback and filled with the extra buffers if there are more
     *   buffers than buf[] can hold. extended_buf will be freed in
     *   av_frame_unref().
     *
     * If AV_CODEC_CAP_DR1 is not set then get_buffer2() must call
     * avcodec_default_get_buffer2() instead of providing buffers allocated by
     * some other means.
     *
     * Each data plane must be aligned to the maximum required by the target
     * CPU.
     *
     * @see avcodec_default_get_buffer2()
     *
     * Video:
     *
     * If AV_GET_BUFFER_FLAG_REF is set in flags then the frame may be reused
     * (read and/or written to if it is writable) later by libavcodec.
     *
     * avcodec_align_dimensions2() should be used to find the required width and
     * height, as they normally need to be rounded up to the next multiple of 16.
     *
     * Some decoders do not support linesizes changing between frames.
     *
     * If frame multithreading is used, this callback may be called from a
     * different thread, but not from more than one at once. Does not need to be
     * reentrant.
     *
     * @see avcodec_align_dimensions2()
     *
     * Audio:
     *
     * Decoders request a buffer of a particular size by setting
     * AVFrame.nb_samples prior to calling get_buffer2(). The decoder may,
     * however, utilize only part of the buffer by setting AVFrame.nb_samples
     * to a smaller value in the output frame.
     *
     * As a convenience, av_samples_get_buffer_size() and
     * av_samples_fill_arrays() in libavutil may be used by custom get_buffer2()
     * functions to find the required data size and to fill data pointers and
     * linesize. In AVFrame.linesize, only linesize[0] may be set for audio
     * since all planes must be the same size.
     *
     * @see av_samples_get_buffer_size(), av_samples_fill_arrays()
     *
     * - encoding: unused
     * - decoding: Set by libavcodec, user can override.
     */
    int (*get_buffer2)(struct AVCodecContext *s, AVFrame *frame, int flags);

    /* - encoding parameters */
    float qcompress;  ///< amount of qscale change between easy & hard scenes (0.0-1.0)
    float qblur;      ///< amount of qscale smoothing over time (0.0-1.0)

    /**
     * minimum quantizer
     * - encoding: Set by user.
     * - decoding: unused
     */
    int qmin;

    /**
     * maximum quantizer
     * - encoding: Set by user.
     * - decoding: unused
     */
    int qmax;

    /**
     * maximum quantizer difference between frames
     * - encoding: Set by user.
     * - decoding: unused
     */
    int max_qdiff;

    /**
     * decoder bitstream buffer size
     * - encoding: Set by user.
     * - decoding: unused
     */
    int rc_buffer_size;

    /**
     * ratecontrol override, see RcOverride
     * - encoding: Allocated/set/freed by user.
     * - decoding: unused
     */
    int rc_override_count;
    RcOverride *rc_override;

    /**
     * maximum bitrate
     * - encoding: Set by user.
     * - decoding: Set by user, may be overwritten by libavcodec.
     */
    int64_t rc_max_rate;

    /**
     * minimum bitrate
     * - encoding: Set by user.
     * - decoding: unused
     */
    int64_t rc_min_rate;

    /**
     * Ratecontrol attempt to use, at maximum, <value> of what can be used without an underflow.
     * - encoding: Set by user.
     * - decoding: unused.
     */
    float rc_max_available_vbv_use;

    /**
     * Ratecontrol attempt to use, at least, <value> times the amount needed to prevent a vbv overflow.
     * - encoding: Set by user.
     * - decoding: unused.
     */
    float rc_min_vbv_overflow_use;

    /**
     * Number of bits which should be loaded into the rc buffer before decoding starts.
     * - encoding: Set by user.
     * - decoding: unused
     */
    int rc_initial_buffer_occupancy;

    /**
     * trellis RD quantization
     * - encoding: Set by user.
     * - decoding: unused
     */
    int trellis;

    /**
     * pass1 encoding statistics output buffer
     * - encoding: Set by libavcodec.
     * - decoding: unused
     */
    char *stats_out;

    /**
     * pass2 encoding statistics input buffer
     * Concatenated stuff from stats_out of pass1 should be placed here.
     * - encoding: Allocated/set/freed by user.
     * - decoding: unused
     */
    char *stats_in;

    /**
     * Work around bugs in encoders which sometimes cannot be detected automatically.
     * - encoding: Set by user
     * - decoding: Set by user
     */
    int workaround_bugs;
#define FF_BUG_AUTODETECT       1  ///< autodetection
#define FF_BUG_XVID_ILACE       4
#define FF_BUG_UMP4             8
#define FF_BUG_NO_PADDING       16
#define FF_BUG_AMV              32
#define FF_BUG_QPEL_CHROMA      64
#define FF_BUG_STD_QPEL         128
#define FF_BUG_QPEL_CHROMA2     256
#define FF_BUG_DIRECT_BLOCKSIZE 512
#define FF_BUG_EDGE             1024
#define FF_BUG_HPEL_CHROMA      2048
#define FF_BUG_DC_CLIP          4096
#define FF_BUG_MS               8192 ///< Work around various bugs in Microsoft's broken decoders.
#define FF_BUG_TRUNCATED       16384
#define FF_BUG_IEDGE           32768

    /**
     * strictly follow the standard (MPEG-4, ...).
     * - encoding: Set by user.
     * - decoding: Set by user.
     * Setting this to STRICT or higher means the encoder and decoder will
     * generally do stupid things, whereas setting it to unofficial or lower
     * will mean the encoder might produce output that is not supported by all
     * spec-compliant decoders. Decoders don't differentiate between normal,
     * unofficial and experimental (that is, they always try to decode things
     * when they can) unless they are explicitly asked to behave stupidly
     * (=strictly conform to the specs)
     */
    int strict_std_compliance;
#define FF_COMPLIANCE_VERY_STRICT   2 ///< Strictly conform to an older more strict version of the spec or reference software.
#define FF_COMPLIANCE_STRICT        1 ///< Strictly conform to all the things in the spec no matter what consequences.
#define FF_COMPLIANCE_NORMAL        0
#define FF_COMPLIANCE_UNOFFICIAL   -1 ///< Allow unofficial extensions
#define FF_COMPLIANCE_EXPERIMENTAL -2 ///< Allow nonstandardized experimental things.

    /**
     * error concealment flags
     * - encoding: unused
     * - decoding: Set by user.
     */
    int error_concealment;
#define FF_EC_GUESS_MVS   1
#define FF_EC_DEBLOCK     2
#define FF_EC_FAVOR_INTER 256

    /**
     * debug
     * - encoding: Set by user.
     * - decoding: Set by user.
     */
    int debug;
#define FF_DEBUG_PICT_INFO   1
#define FF_DEBUG_RC          2
#define FF_DEBUG_BITSTREAM   4
#define FF_DEBUG_MB_TYPE     8
#define FF_DEBUG_QP          16
#define FF_DEBUG_DCT_COEFF   0x00000040
#define FF_DEBUG_SKIP        0x00000080
#define FF_DEBUG_STARTCODE   0x00000100
#define FF_DEBUG_ER          0x00000400
#define FF_DEBUG_MMCO        0x00000800
#define FF_DEBUG_BUGS        0x00001000
#define FF_DEBUG_BUFFERS     0x00008000
#define FF_DEBUG_THREADS     0x00010000
#define FF_DEBUG_GREEN_MD    0x00800000
#define FF_DEBUG_NOMC        0x01000000

    /**
     * Error recognition; may misdetect some more or less valid parts as errors.
     * - encoding: Set by user.
     * - decoding: Set by user.
     */
    int err_recognition;

/**
 * Verify checksums embedded in the bitstream (could be of either encoded or
 * decoded data, depending on the codec) and print an error message on mismatch.
 * If AV_EF_EXPLODE is also set, a mismatching checksum will result in the
 * decoder returning an error.
 */
#define AV_EF_CRCCHECK  (1<<0)
#define AV_EF_BITSTREAM (1<<1)          ///< detect bitstream specification deviations
#define AV_EF_BUFFER    (1<<2)          ///< detect improper bitstream length
#define AV_EF_EXPLODE   (1<<3)          ///< abort decoding on minor error detection

#define AV_EF_IGNORE_ERR (1<<15)        ///< ignore errors and continue
#define AV_EF_CAREFUL    (1<<16)        ///< consider things that violate the spec, are fast to calculate and have not been seen in the wild as errors
#define AV_EF_COMPLIANT  (1<<17)        ///< consider all spec non compliances as errors
#define AV_EF_AGGRESSIVE (1<<18)        ///< consider things that a sane encoder should not do as an error


    /**
     * opaque 64-bit number (generally a PTS) that will be reordered and
     * output in AVFrame.reordered_opaque
     * - encoding: Set by libavcodec to the reordered_opaque of the input
     *             frame corresponding to the last returned packet. Only
     *             supported by encoders with the
     *             AV_CODEC_CAP_ENCODER_REORDERED_OPAQUE capability.
     * - decoding: Set by user.
     */
    int64_t reordered_opaque;

    /**
     * Hardware accelerator in use
     * - encoding: unused.
     * - decoding: Set by libavcodec
     */
    const struct AVHWAccel *hwaccel;

    /**
     * Hardware accelerator context.
     * For some hardware accelerators, a global context needs to be
     * provided by the user. In that case, this holds display-dependent
     * data FFmpeg cannot instantiate itself. Please refer to the
     * FFmpeg HW accelerator documentation to know how to fill this.
     * - encoding: unused
     * - decoding: Set by user
     */
    void *hwaccel_context;

    /**
     * error
     * - encoding: Set by libavcodec if flags & AV_CODEC_FLAG_PSNR.
     * - decoding: unused
     */
    uint64_t error[AV_NUM_DATA_POINTERS];

    /**
     * DCT algorithm, see FF_DCT_* below
     * - encoding: Set by user.
     * - decoding: unused
     */
    int dct_algo;
#define FF_DCT_AUTO    0
#define FF_DCT_FASTINT 1
#define FF_DCT_INT     2
#define FF_DCT_MMX     3
#define FF_DCT_ALTIVEC 5
#define FF_DCT_FAAN    6

    /**
     * IDCT algorithm, see FF_IDCT_* below.
     * - encoding: Set by user.
     * - decoding: Set by user.
     */
    int idct_algo;
#define FF_IDCT_AUTO          0
#define FF_IDCT_INT           1
#define FF_IDCT_SIMPLE        2
#define FF_IDCT_SIMPLEMMX     3
#define FF_IDCT_ARM           7
#define FF_IDCT_ALTIVEC       8
#define FF_IDCT_SIMPLEARM     10
#define FF_IDCT_XVID          14
#define FF_IDCT_SIMPLEARMV5TE 16
#define FF_IDCT_SIMPLEARMV6   17
#define FF_IDCT_FAAN          20
#define FF_IDCT_SIMPLENEON    22
#if FF_API_IDCT_NONE
// formerly used by xvmc
#define FF_IDCT_NONE          24
#endif
#define FF_IDCT_SIMPLEAUTO    128

    /**
     * bits per sample/pixel from the demuxer (needed for huffyuv).
     * - encoding: Set by libavcodec.
     * - decoding: Set by user.
     */
     int bits_per_coded_sample;

    /**
     * Bits per sample/pixel of internal libavcodec pixel/sample format.
     * - encoding: set by user.
     * - decoding: set by libavcodec.
     */
    int bits_per_raw_sample;

    /**
     * low resolution decoding, 1-> 1/2 size, 2->1/4 size
     * - encoding: unused
     * - decoding: Set by user.
     */
     int lowres;

    /**
     * thread count
     * is used to decide how many independent tasks should be passed to execute()
     * - encoding: Set by user.
     * - decoding: Set by user.
     */
    int thread_count;

    /**
     * Which multithreading methods to use.
     * Use of FF_THREAD_FRAME will increase decoding delay by one frame per thread,
     * so clients which cannot provide future frames should not use it.
     *
     * - encoding: Set by user, otherwise the default is used.
     * - decoding: Set by user, otherwise the default is used.
     */
    int thread_type;
#define FF_THREAD_FRAME   1 ///< Decode more than one frame at once
#define FF_THREAD_SLICE   2 ///< Decode more than one part of a single frame at once

    /**
     * Which multithreading methods are in use by the codec.
     * - encoding: Set by libavcodec.
     * - decoding: Set by libavcodec.
     */
    int active_thread_type;

#if FF_API_THREAD_SAFE_CALLBACKS
    /**
     * Set by the client if its custom get_buffer() callback can be called
     * synchronously from another thread, which allows faster multithreaded decoding.
     * draw_horiz_band() will be called from other threads regardless of this setting.
     * Ignored if the default get_buffer() is used.
     * - encoding: Set by user.
     * - decoding: Set by user.
     *
     * @deprecated the custom get_buffer2() callback should always be
     *   thread-safe. Thread-unsafe get_buffer2() implementations will be
     *   invalid starting with LIBAVCODEC_VERSION_MAJOR=60; in other words,
     *   libavcodec will behave as if this field was always set to 1.
     *   Callers that want to be forward compatible with future libavcodec
     *   versions should wrap access to this field in
     *     #if LIBAVCODEC_VERSION_MAJOR < 60
     */
    attribute_deprecated
    int thread_safe_callbacks;
#endif

    /**
     * The codec may call this to execute several independent things.
     * It will return only after finishing all tasks.
     * The user may replace this with some multithreaded implementation,
     * the default implementation will execute the parts serially.
     * @param count the number of things to execute
     * - encoding: Set by libavcodec, user can override.
     * - decoding: Set by libavcodec, user can override.
     */
    int (*execute)(struct AVCodecContext *c, int (*func)(struct AVCodecContext *c2, void *arg), void *arg2, int *ret, int count, int size);

    /**
     * The codec may call this to execute several independent things.
     * It will return only after finishing all tasks.
     * The user may replace this with some multithreaded implementation,
     * the default implementation will execute the parts serially.
     * @param c context passed also to func
     * @param count the number of things to execute
     * @param arg2 argument passed unchanged to func
     * @param ret return values of executed functions, must have space for "count" values. May be NULL.
     * @param func function that will be called count times, with jobnr from 0 to count-1.
     *             threadnr will be in the range 0 to c->thread_count-1 < MAX_THREADS and so that no
     *             two instances of func executing at the same time will have the same threadnr.
     * @return always 0 currently, but code should handle a future improvement where when any call to func
     *         returns < 0 no further calls to func may be done and < 0 is returned.
     * - encoding: Set by libavcodec, user can override.
     * - decoding: Set by libavcodec, user can override.
     */
    int (*execute2)(struct AVCodecContext *c, int (*func)(struct AVCodecContext *c2, void *arg, int jobnr, int threadnr), void *arg2, int *ret, int count);

    /**
     * noise vs. sse weight for the nsse comparison function
     * - encoding: Set by user.
     * - decoding: unused
     */
     int nsse_weight;

    /**
     * profile
     * - encoding: Set by user.
     * - decoding: Set by libavcodec.
     */
     int profile;
#define FF_PROFILE_UNKNOWN -99
#define FF_PROFILE_RESERVED -100

#define FF_PROFILE_AAC_MAIN 0
#define FF_PROFILE_AAC_LOW  1
#define FF_PROFILE_AAC_SSR  2
#define FF_PROFILE_AAC_LTP  3
#define FF_PROFILE_AAC_HE   4
#define FF_PROFILE_AAC_HE_V2 28
#define FF_PROFILE_AAC_LD   22
#define FF_PROFILE_AAC_ELD  38
#define FF_PROFILE_MPEG2_AAC_LOW 128
#define FF_PROFILE_MPEG2_AAC_HE  131

#define FF_PROFILE_DNXHD         0
#define FF_PROFILE_DNXHR_LB      1
#define FF_PROFILE_DNXHR_SQ      2
#define FF_PROFILE_DNXHR_HQ      3
#define FF_PROFILE_DNXHR_HQX     4
#define FF_PROFILE_DNXHR_444     5

#define FF_PROFILE_DTS         20
#define FF_PROFILE_DTS_ES      30
#define FF_PROFILE_DTS_96_24   40
#define FF_PROFILE_DTS_HD_HRA  50
#define FF_PROFILE_DTS_HD_MA   60
#define FF_PROFILE_DTS_EXPRESS 70

#define FF_PROFILE_MPEG2_422    0
#define FF_PROFILE_MPEG2_HIGH   1
#define FF_PROFILE_MPEG2_SS     2
#define FF_PROFILE_MPEG2_SNR_SCALABLE  3
#define FF_PROFILE_MPEG2_MAIN   4
#define FF_PROFILE_MPEG2_SIMPLE 5

#define FF_PROFILE_H264_CONSTRAINED  (1<<9)  // 8+1; constraint_set1_flag
#define FF_PROFILE_H264_INTRA        (1<<11) // 8+3; constraint_set3_flag

#define FF_PROFILE_H264_BASELINE             66
#define FF_PROFILE_H264_CONSTRAINED_BASELINE (66|FF_PROFILE_H264_CONSTRAINED)
#define FF_PROFILE_H264_MAIN                 77
#define FF_PROFILE_H264_EXTENDED             88
#define FF_PROFILE_H264_HIGH                 100
#define FF_PROFILE_H264_HIGH_10              110
#define FF_PROFILE_H264_HIGH_10_INTRA        (110|FF_PROFILE_H264_INTRA)
#define FF_PROFILE_H264_MULTIVIEW_HIGH       118
#define FF_PROFILE_H264_HIGH_422             122
#define FF_PROFILE_H264_HIGH_422_INTRA       (122|FF_PROFILE_H264_INTRA)
#define FF_PROFILE_H264_STEREO_HIGH          128
#define FF_PROFILE_H264_HIGH_444             144
#define FF_PROFILE_H264_HIGH_444_PREDICTIVE  244
#define FF_PROFILE_H264_HIGH_444_INTRA       (244|FF_PROFILE_H264_INTRA)
#define FF_PROFILE_H264_CAVLC_444            44

#define FF_PROFILE_VC1_SIMPLE   0
#define FF_PROFILE_VC1_MAIN     1
#define FF_PROFILE_VC1_COMPLEX  2
#define FF_PROFILE_VC1_ADVANCED 3

#define FF_PROFILE_MPEG4_SIMPLE                     0
#define FF_PROFILE_MPEG4_SIMPLE_SCALABLE            1
#define FF_PROFILE_MPEG4_CORE                       2
#define FF_PROFILE_MPEG4_MAIN                       3
#define FF_PROFILE_MPEG4_N_BIT                      4
#define FF_PROFILE_MPEG4_SCALABLE_TEXTURE           5
#define FF_PROFILE_MPEG4_SIMPLE_FACE_ANIMATION      6
#define FF_PROFILE_MPEG4_BASIC_ANIMATED_TEXTURE     7
#define FF_PROFILE_MPEG4_HYBRID                     8
#define FF_PROFILE_MPEG4_ADVANCED_REAL_TIME         9
#define FF_PROFILE_MPEG4_CORE_SCALABLE             10
#define FF_PROFILE_MPEG4_ADVANCED_CODING           11
#define FF_PROFILE_MPEG4_ADVANCED_CORE             12
#define FF_PROFILE_MPEG4_ADVANCED_SCALABLE_TEXTURE 13
#define FF_PROFILE_MPEG4_SIMPLE_STUDIO             14
#define FF_PROFILE_MPEG4_ADVANCED_SIMPLE           15

#define FF_PROFILE_JPEG2000_CSTREAM_RESTRICTION_0   1
#define FF_PROFILE_JPEG2000_CSTREAM_RESTRICTION_1   2
#define FF_PROFILE_JPEG2000_CSTREAM_NO_RESTRICTION  32768
#define FF_PROFILE_JPEG2000_DCINEMA_2K              3
#define FF_PROFILE_JPEG2000_DCINEMA_4K              4

#define FF_PROFILE_VP9_0                            0
#define FF_PROFILE_VP9_1                            1
#define FF_PROFILE_VP9_2                            2
#define FF_PROFILE_VP9_3                            3

#define FF_PROFILE_HEVC_MAIN                        1
#define FF_PROFILE_HEVC_MAIN_10                     2
#define FF_PROFILE_HEVC_MAIN_STILL_PICTURE          3
#define FF_PROFILE_HEVC_REXT                        4

#define FF_PROFILE_VVC_MAIN_10                      1
#define FF_PROFILE_VVC_MAIN_10_444                 33

#define FF_PROFILE_AV1_MAIN                         0
#define FF_PROFILE_AV1_HIGH                         1
#define FF_PROFILE_AV1_PROFESSIONAL                 2

#define FF_PROFILE_MJPEG_HUFFMAN_BASELINE_DCT            0xc0
#define FF_PROFILE_MJPEG_HUFFMAN_EXTENDED_SEQUENTIAL_DCT 0xc1
#define FF_PROFILE_MJPEG_HUFFMAN_PROGRESSIVE_DCT         0xc2
#define FF_PROFILE_MJPEG_HUFFMAN_LOSSLESS                0xc3
#define FF_PROFILE_MJPEG_JPEG_LS                         0xf7

#define FF_PROFILE_SBC_MSBC                         1

#define FF_PROFILE_PRORES_PROXY     0
#define FF_PROFILE_PRORES_LT        1
#define FF_PROFILE_PRORES_STANDARD  2
#define FF_PROFILE_PRORES_HQ        3
#define FF_PROFILE_PRORES_4444      4
#define FF_PROFILE_PRORES_XQ        5

#define FF_PROFILE_ARIB_PROFILE_A 0
#define FF_PROFILE_ARIB_PROFILE_C 1

#define FF_PROFILE_KLVA_SYNC 0
#define FF_PROFILE_KLVA_ASYNC 1

    /**
     * level
     * - encoding: Set by user.
     * - decoding: Set by libavcodec.
     */
     int level;
#define FF_LEVEL_UNKNOWN -99

    /**
     * Skip loop filtering for selected frames.
     * - encoding: unused
     * - decoding: Set by user.
     */
    enum AVDiscard skip_loop_filter;

    /**
     * Skip IDCT/dequantization for selected frames.
     * - encoding: unused
     * - decoding: Set by user.
     */
    enum AVDiscard skip_idct;

    /**
     * Skip decoding for selected frames.
     * - encoding: unused
     * - decoding: Set by user.
     */
    enum AVDiscard skip_frame;

    /**
     * Header containing style information for text subtitles.
     * For SUBTITLE_ASS subtitle type, it should contain the whole ASS
     * [Script Info] and [V4+ Styles] section, plus the [Events] line and
     * the Format line following. It shouldn't include any Dialogue line.
     * - encoding: Set/allocated/freed by user (before avcodec_open2())
     * - decoding: Set/allocated/freed by libavcodec (by avcodec_open2())
     */
    uint8_t *subtitle_header;
    int subtitle_header_size;

    /**
     * Audio only. The number of "priming" samples (padding) inserted by the
     * encoder at the beginning of the audio. I.e. this number of leading
     * decoded samples must be discarded by the caller to get the original audio
     * without leading padding.
     *
     * - decoding: unused
     * - encoding: Set by libavcodec. The timestamps on the output packets are
     *             adjusted by the encoder so that they always refer to the
     *             first sample of the data actually contained in the packet,
     *             including any added padding.  E.g. if the timebase is
     *             1/samplerate and the timestamp of the first input sample is
     *             0, the timestamp of the first output packet will be
     *             -initial_padding.
     */
    int initial_padding;

    /**
     * - decoding: For codecs that store a framerate value in the compressed
     *             bitstream, the decoder may export it here. { 0, 1} when
     *             unknown.
     * - encoding: May be used to signal the framerate of CFR content to an
     *             encoder.
     */
    AVRational framerate;

    /**
     * 标称非加速像素格式，参见AV_PIX_FMT_xxx。
     * - encoding: unused.
     * - decoding: Set by libavcodec before calling get_format()
     */
    enum AVPixelFormat sw_pix_fmt;

    /**
     * Timebase in which pkt_dts/pts and AVPacket.dts/pts are.
     * - encoding unused.
     * - decoding set by user.
     */
    AVRational pkt_timebase;

    /**
     * AVCodecDescriptor
     * - encoding: unused.
     * - decoding: set by libavcodec.
     */
    const AVCodecDescriptor *codec_descriptor;

    /**
     * Current statistics for PTS correction.
     * - decoding: maintained and used by libavcodec, not intended to be used by user apps
     * - encoding: unused
     */
    int64_t pts_correction_num_faulty_pts; /// Number of incorrect PTS values so far
    int64_t pts_correction_num_faulty_dts; /// Number of incorrect DTS values so far
    int64_t pts_correction_last_pts;       /// PTS of the last frame
    int64_t pts_correction_last_dts;       /// DTS of the last frame

    /**
     * Character encoding of the input subtitles file.
     * - decoding: set by user
     * - encoding: unused
     */
    char *sub_charenc;

    /**
     * Subtitles character encoding mode. Formats or codecs might be adjusting
     * this setting (if they are doing the conversion themselves for instance).
     * - decoding: set by libavcodec
     * - encoding: unused
     */
    int sub_charenc_mode;
#define FF_SUB_CHARENC_MODE_DO_NOTHING  -1  ///< do nothing (demuxer outputs a stream supposed to be already in UTF-8, or the codec is bitmap for instance)
#define FF_SUB_CHARENC_MODE_AUTOMATIC    0  ///< libavcodec will select the mode itself
#define FF_SUB_CHARENC_MODE_PRE_DECODER  1  ///< the AVPacket data needs to be recoded to UTF-8 before being fed to the decoder, requires iconv
#define FF_SUB_CHARENC_MODE_IGNORE       2  ///< neither convert the subtitles, nor check them for valid UTF-8

    /**
     * Skip processing alpha if supported by codec.
     * Note that if the format uses pre-multiplied alpha (common with VP6,
     * and recommended due to better video quality/compression)
     * the image will look as if alpha-blended onto a black background.
     * However for formats that do not use pre-multiplied alpha
     * there might be serious artefacts (though e.g. libswscale currently
     * assumes pre-multiplied alpha anyway).
     *
     * - decoding: set by user
     * - encoding: unused
     */
    int skip_alpha;

    /**
     * Number of samples to skip after a discontinuity
     * - decoding: unused
     * - encoding: set by libavcodec
     */
    int seek_preroll;

#if FF_API_DEBUG_MV
    /**
     * @deprecated unused
     */
    attribute_deprecated
    int debug_mv;
#define FF_DEBUG_VIS_MV_P_FOR  0x00000001 //visualize forward predicted MVs of P frames
#define FF_DEBUG_VIS_MV_B_FOR  0x00000002 //visualize forward predicted MVs of B frames
#define FF_DEBUG_VIS_MV_B_BACK 0x00000004 //visualize backward predicted MVs of B frames
#endif

    /**
     * custom intra quantization matrix
     * - encoding: Set by user, can be NULL.
     * - decoding: unused.
     */
    uint16_t *chroma_intra_matrix;

    /**
     * dump format separator.
     * can be ", " or "\n      " or anything else
     * - encoding: Set by user.
     * - decoding: Set by user.
     */
    uint8_t *dump_separator;

    /**
     * ',' separated list of allowed decoders.
     * If NULL then all are allowed
     * - encoding: unused
     * - decoding: set by user
     */
    char *codec_whitelist;

    /**
     * Properties of the stream that gets decoded
     * - encoding: unused
     * - decoding: set by libavcodec
     */
    unsigned properties;
#define FF_CODEC_PROPERTY_LOSSLESS        0x00000001
#define FF_CODEC_PROPERTY_CLOSED_CAPTIONS 0x00000002
#define FF_CODEC_PROPERTY_FILM_GRAIN      0x00000004

    /**
     * Additional data associated with the entire coded stream.
     *
     * - decoding: unused
     * - encoding: may be set by libavcodec after avcodec_open2().
     */
    AVPacketSideData *coded_side_data;
    int            nb_coded_side_data;

    /**
     * A reference to the AVHWFramesContext describing the input (for encoding)
     * or output (decoding) frames. The reference is set by the caller and
     * afterwards owned (and freed) by libavcodec - it should never be read by
     * the caller after being set.
     *
     * - decoding: This field should be set by the caller from the get_format()
     *             callback. The previous reference (if any) will always be
     *             unreffed by libavcodec before the get_format() call.
     *
     *             If the default get_buffer2() is used with a hwaccel pixel
     *             format, then this AVHWFramesContext will be used for
     *             allocating the frame buffers.
     *
     * - encoding: For hardware encoders configured to use a hwaccel pixel
     *             format, this field should be set by the caller to a reference
     *             to the AVHWFramesContext describing input frames.
     *             AVHWFramesContext.format must be equal to
     *             AVCodecContext.pix_fmt.
     *
     *             This field should be set before avcodec_open2() is called.
     */
    AVBufferRef *hw_frames_ctx;

#if FF_API_SUB_TEXT_FORMAT
    /**
     * @deprecated unused
     */
    attribute_deprecated
    int sub_text_format;
#define FF_SUB_TEXT_FMT_ASS              0
#endif

    /**
     * Audio only. The amount of padding (in samples) appended by the encoder to
     * the end of the audio. I.e. this number of decoded samples must be
     * discarded by the caller from the end of the stream to get the original
     * audio without any trailing padding.
     *
     * - decoding: unused
     * - encoding: unused
     */
    int trailing_padding;

    /**
     * The number of pixels per image to maximally accept.
     *
     * - decoding: set by user
     * - encoding: set by user
     */
    int64_t max_pixels;

    /**
     * 对AVHWDeviceContext的引用，描述硬件编码器/解码器将使用的设备。
     * 引用由调用者设置，然后由libavcodec拥有(并释放)。
     *
     * This should be used if either the codec device does not require
     * hardware frames or any that are used are to be allocated internally by
     * libavcodec.  If the user wishes to supply any of the frames used as
     * encoder input or decoder output then hw_frames_ctx should be used
     * instead.  When hw_frames_ctx is set in get_format() for a decoder, this
     * field will be ignored while decoding the associated stream segment, but
     * may again be used on a following one after another get_format() call.
     *
     * For both encoders and decoders this field should be set before
     * avcodec_open2() is called and must not be written to thereafter.
     *
     * Note that some decoders may require this field to be set initially in
     * order to support hw_frames_ctx at all - in that case, all frames
     * contexts used must be created on the same device.
     */
    AVBufferRef *hw_device_ctx;

    /**
     * Bit set of AV_HWACCEL_FLAG_* flags, which affect hardware accelerated
     * decoding (if active).
     * - encoding: unused
     * - decoding: Set by user (either before avcodec_open2(), or in the
     *             AVCodecContext.get_format callback)
     */
    int hwaccel_flags;

    /**
     * Video decoding only. Certain video codecs support cropping, meaning that
     * only a sub-rectangle of the decoded frame is intended for display.  This
     * option controls how cropping is handled by libavcodec.
     *
     * When set to 1 (the default), libavcodec will apply cropping internally.
     * I.e. it will modify the output frame width/height fields and offset the
     * data pointers (only by as much as possible while preserving alignment, or
     * by the full amount if the AV_CODEC_FLAG_UNALIGNED flag is set) so that
     * the frames output by the decoder refer only to the cropped area. The
     * crop_* fields of the output frames will be zero.
     *
     * When set to 0, the width/height fields of the output frames will be set
     * to the coded dimensions and the crop_* fields will describe the cropping
     * rectangle. Applying the cropping is left to the caller.
     *
     * @warning When hardware acceleration with opaque output frames is used,
     * libavcodec is unable to apply cropping from the top/left border.
     *
     * @note when this option is set to zero, the width/height fields of the
     * AVCodecContext and output AVFrames have different meanings. The codec
     * context fields store display dimensions (with the coded dimensions in
     * coded_width/height), while the frame fields store the coded dimensions
     * (with the display dimensions being determined by the crop_* fields).
     */
    int apply_cropping;

    /*
     * Video decoding only.  Sets the number of extra hardware frames which
     * the decoder will allocate for use by the caller.  This must be set
     * before avcodec_open2() is called.
     *
     * Some hardware decoders require all frames that they will use for
     * output to be defined in advance before decoding starts.  For such
     * decoders, the hardware frame pool must therefore be of a fixed size.
     * The extra frames set here are on top of any number that the decoder
     * needs internally in order to operate normally (for example, frames
     * used as reference pictures).
     */
    int extra_hw_frames;

    /**
     * The percentage of damaged samples to discard a frame.
     *
     * - decoding: set by user
     * - encoding: unused
     */
    int discard_damaged_percentage;

    /**
     * The number of samples per frame to maximally accept.
     *
     * - decoding: set by user
     * - encoding: set by user
     */
    int64_t max_samples;

    /**
     * Bit set of AV_CODEC_EXPORT_DATA_* flags, which affects the kind of
     * metadata exported in frame, packet, or coded stream side data by
     * decoders and encoders.
     *
     * - decoding: set by user
     * - encoding: set by user
     */
    int export_side_data;

    /**
     * This callback is called at the beginning of each packet to get a data
     * buffer for it.
     *
     * The following field will be set in the packet before this callback is
     * called:
     * - size
     * This callback must use the above value to calculate the required buffer size,
     * which must padded by at least AV_INPUT_BUFFER_PADDING_SIZE bytes.
     *
     * In some specific cases, the encoder may not use the entire buffer allocated by this
     * callback. This will be reflected in the size value in the packet once returned by
     * avcodec_receive_packet().
     *
     * This callback must fill the following fields in the packet:
     * - data: alignment requirements for AVPacket apply, if any. Some architectures and
     *   encoders may benefit from having aligned data.
     * - buf: must contain a pointer to an AVBufferRef structure. The packet's
     *   data pointer must be contained in it. See: av_buffer_create(), av_buffer_alloc(),
     *   and av_buffer_ref().
     *
     * If AV_CODEC_CAP_DR1 is not set then get_encode_buffer() must call
     * avcodec_default_get_encode_buffer() instead of providing a buffer allocated by
     * some other means.
     *
     * The flags field may contain a combination of AV_GET_ENCODE_BUFFER_FLAG_ flags.
     * They may be used for example to hint what use the buffer may get after being
     * created.
     * Implementations of this callback may ignore flags they don't understand.
     * If AV_GET_ENCODE_BUFFER_FLAG_REF is set in flags then the packet may be reused
     * (read and/or written to if it is writable) later by libavcodec.
     *
     * This callback must be thread-safe, as when frame threading is used, it may
     * be called from multiple threads simultaneously.
     *
     * @see avcodec_default_get_encode_buffer()
     *
     * - encoding: Set by libavcodec, user can override.
     * - decoding: unused
     */
    int (*get_encode_buffer)(struct AVCodecContext *s, AVPacket *pkt, int flags);

    /**
     * Audio channel layout.
     * - encoding: must be set by the caller, to one of AVCodec.ch_layouts.
     * - decoding: may be set by the caller if known e.g. from the container.
     *             The decoder can then override during decoding as needed.
     */
    AVChannelLayout ch_layout;
} AVCodecContext;

/**
 * @defgroup lavc_hwaccel AVHWAccel
 *
 * @note  Nothing in this structure should be accessed by the user.  At some
 *        point in future it will not be externally visible at all.
 *
 * @{
 */
typedef struct AVHWAccel {
    /**
     * Name of the hardware accelerated codec.
     * The name is globally unique among encoders and among decoders (but an
     * encoder and a decoder can share the same name).
     */
    const char *name;

    /**
     * Type of codec implemented by the hardware accelerator.
     *
     * See AVMEDIA_TYPE_xxx
     */
    enum AVMediaType type;

    /**
     * Codec implemented by the hardware accelerator.
     *
     * See AV_CODEC_ID_xxx
     */
    enum AVCodecID id;

    /**
     * Supported pixel format.
     *
     * Only hardware accelerated formats are supported here.
     */
    enum AVPixelFormat pix_fmt;

    /**
     * Hardware accelerated codec capabilities.
     * see AV_HWACCEL_CODEC_CAP_*
     */
    int capabilities;

    /*****************************************************************
     * No fields below this line are part of the public API. They
     * may not be used outside of libavcodec and can be changed and
     * removed at will.
     * New public fields should be added right above.
     *****************************************************************
     */

    /**
     * Allocate a custom buffer
     */
    int (*alloc_frame)(AVCodecContext *avctx, AVFrame *frame);

    /**
     * Called at the beginning of each frame or field picture.
     *
     * Meaningful frame information (codec specific) is guaranteed to
     * be parsed at this point. This function is mandatory.
     *
     * Note that buf can be NULL along with buf_size set to 0.
     * Otherwise, this means the whole frame is available at this point.
     *
     * @param avctx the codec context
     * @param buf the frame data buffer base
     * @param buf_size the size of the frame in bytes
     * @return zero if successful, a negative value otherwise
     */
    int (*start_frame)(AVCodecContext *avctx, const uint8_t *buf, uint32_t buf_size);

    /**
     * Callback for parameter data (SPS/PPS/VPS etc).
     *
     * Useful for hardware decoders which keep persistent state about the
     * video parameters, and need to receive any changes to update that state.
     *
     * @param avctx the codec context
     * @param type the nal unit type
     * @param buf the nal unit data buffer
     * @param buf_size the size of the nal unit in bytes
     * @return zero if successful, a negative value otherwise
     */
    int (*decode_params)(AVCodecContext *avctx, int type, const uint8_t *buf, uint32_t buf_size);

    /**
     * Callback for each slice.
     *
     * Meaningful slice information (codec specific) is guaranteed to
     * be parsed at this point. This function is mandatory.
     *
     * @param avctx the codec context
     * @param buf the slice data buffer base
     * @param buf_size the size of the slice in bytes
     * @return zero if successful, a negative value otherwise
     */
    int (*decode_slice)(AVCodecContext *avctx, const uint8_t *buf, uint32_t buf_size);

    /**
     * Called at the end of each frame or field picture.
     *
     * The whole picture is parsed at this point and can now be sent
     * to the hardware accelerator. This function is mandatory.
     *
     * @param avctx the codec context
     * @return zero if successful, a negative value otherwise
     */
    int (*end_frame)(AVCodecContext *avctx);

    /**
     * Size of per-frame hardware accelerator private data.
     *
     * Private data is allocated with av_mallocz() before
     * AVCodecContext.get_buffer() and deallocated after
     * AVCodecContext.release_buffer().
     */
    int frame_priv_data_size;

    /**
     * Initialize the hwaccel private data.
     *
     * This will be called from ff_get_format(), after hwaccel and
     * hwaccel_context are set and the hwaccel private data in AVCodecInternal
     * is allocated.
     */
    int (*init)(AVCodecContext *avctx);

    /**
     * Uninitialize the hwaccel private data.
     *
     * This will be called from get_format() or avcodec_close(), after hwaccel
     * and hwaccel_context are already uninitialized.
     */
    int (*uninit)(AVCodecContext *avctx);

    /**
     * Size of the private data to allocate in
     * AVCodecInternal.hwaccel_priv_data.
     */
    int priv_data_size;

    /**
     * Internal hwaccel capabilities.
     */
    int caps_internal;

    /**
     * Fill the given hw_frames context with current codec parameters. Called
     * from get_format. Refer to avcodec_get_hw_frames_parameters() for
     * details.
     *
     * This CAN be called before AVHWAccel.init is called, and you must assume
     * that avctx->hwaccel_priv_data is invalid.
     */
    int (*frame_params)(AVCodecContext *avctx, AVBufferRef *hw_frames_ctx);
} AVHWAccel;

/**
 * HWAccel is experimental and is thus avoided in favor of non experimental
 * codecs
 */
#define AV_HWACCEL_CODEC_CAP_EXPERIMENTAL 0x0200

/**
 * Hardware acceleration should be used for decoding even if the codec level
 * used is unknown or higher than the maximum supported level reported by the
 * hardware driver.
 *
 * It's generally a good idea to pass this flag unless you have a specific
 * reason not to, as hardware tends to under-report supported levels.
 */
#define AV_HWACCEL_FLAG_IGNORE_LEVEL (1 << 0)

/**
 * Hardware acceleration can output YUV pixel formats with a different chroma
 * sampling than 4:2:0 and/or other than 8 bits per component.
 */
#define AV_HWACCEL_FLAG_ALLOW_HIGH_DEPTH (1 << 1)

/**
 * Hardware acceleration should still be attempted for decoding when the
 * codec profile does not match the reported capabilities of the hardware.
 *
 * For example, this can be used to try to decode baseline profile H.264
 * streams in hardware - it will often succeed, because many streams marked
 * as baseline profile actually conform to constrained baseline profile.
 *
 * @warning If the stream is actually not supported then the behaviour is
 *          undefined, and may include returning entirely incorrect output
 *          while indicating success.
 */
#define AV_HWACCEL_FLAG_ALLOW_PROFILE_MISMATCH (1 << 2)

/**
 * @}
 */

enum AVSubtitleType {
    SUBTITLE_NONE,

    SUBTITLE_BITMAP,                ///< A bitmap, pict will be set

    /**
     * Plain text, the text field must be set by the decoder and is
     * authoritative. ass and pict fields may contain approximations.
     */
    SUBTITLE_TEXT,

    /**
     * Formatted text, the ass field must be set by the decoder and is
     * authoritative. pict and text fields may contain approximations.
     */
    SUBTITLE_ASS,
};

#define AV_SUBTITLE_FLAG_FORCED 0x00000001

typedef struct AVSubtitleRect {
    int x;         ///< top left corner  of pict, undefined when pict is not set
    int y;         ///< top left corner  of pict, undefined when pict is not set
    int w;         ///< width            of pict, undefined when pict is not set
    int h;         ///< height           of pict, undefined when pict is not set
    int nb_colors; ///< number of colors in pict, undefined when pict is not set

    /**
     * data+linesize for the bitmap of this subtitle.
     * Can be set for text/ass as well once they are rendered.
     */
    uint8_t *data[4];
    int linesize[4];

    enum AVSubtitleType type;

    char *text;                     ///< 0 terminated plain UTF-8 text

    /**
     * 0 terminated ASS/SSA compatible event line.
     * The presentation of this is unaffected by the other values in this
     * struct.
     */
    char *ass;

    int flags;
} AVSubtitleRect;

typedef struct AVSubtitle {
    uint16_t format; /* 0 = graphics */
    uint32_t start_display_time; /* relative to packet pts, in ms */
    uint32_t end_display_time; /* relative to packet pts, in ms */
    unsigned num_rects;
    AVSubtitleRect **rects;
    int64_t pts;    ///< Same as packet pts, in AV_TIME_BASE
} AVSubtitle;

/**
 * Return the LIBAVCODEC_VERSION_INT constant.
 */
unsigned avcodec_version(void);

/**
 * Return the libavcodec build-time configuration.
 */
const char *avcodec_configuration(void);

/**
 * Return the libavcodec license.
 */
const char *avcodec_license(void);

/**
 * 分配AVCodecContext并将其字段设置为默认值。
 * 应使用avcodec_free_context（）释放生成的结构。
 *
 * @param codec 如果非null，为给定的编解码器分配私有数据并初始化默认值。然后用不同的编解码器调用avcodec_open2()是非法的。
 * 如果为NULL，那么特定于编解码器的默认值将不会被初始化，这可能会导致不理想的默认设置(这主要对编码器很重要，例如libx264)。
 *
 * @return AVCodecContext填充了默认值或失败时为NULL。
 */
AVCodecContext *avcodec_alloc_context3(const AVCodec *codec);

/**
 * 释放编解码器上下文和与之相关的所有内容，并将NULL写入提供的指针。
 */
void avcodec_free_context(AVCodecContext **avctx);

/**
 * Get the AVClass for AVCodecContext. It can be used in combination with
 * AV_OPT_SEARCH_FAKE_OBJ for examining options.
 *
 * @see av_opt_find().
 */
const AVClass *avcodec_get_class(void);

#if FF_API_GET_FRAME_CLASS
/**
 * @deprecated This function should not be used.
 */
attribute_deprecated
const AVClass *avcodec_get_frame_class(void);
#endif

/**
 * Get the AVClass for AVSubtitleRect. It can be used in combination with
 * AV_OPT_SEARCH_FAKE_OBJ for examining options.
 *
 * @see av_opt_find().
 */
const AVClass *avcodec_get_subtitle_rect_class(void);

/**
 * Fill the parameters struct based on the values from the supplied codec
 * context. Any allocated fields in par are freed and replaced with duplicates
 * of the corresponding fields in codec.
 *
 * @return >= 0 on success, a negative AVERROR code on failure
 */
int avcodec_parameters_from_context(AVCodecParameters *par,
                                    const AVCodecContext *codec);

/**
 * 根据提供的编解码器参数的值填充编解码器上下文。
 * 在编解码器中，在par中有相应字段的任何已分配字段将被释放，并用par中相应字段的副本替换。
 * 不触及在par中没有对应项的编解码器中的字段。
 *
 * @return >= 0 on success, a negative AVERROR code on failure.
 */
int avcodec_parameters_to_context(AVCodecContext *codec,
                                  const AVCodecParameters *par);

/**
 * 使用给定的AVCodec初始化AVCodecContext。
 * 在使用此函数之前，必须使用avcodec_alloc_context3()来分配上下文。
 *
 * 函数avcodec_find_decoder_by_name()、avcodec_find_encoder_by_name()、
 * avcodec_find_decoder()和avcodec_find_encoder()为检索编解码器提供了一种简单的方法。
 *
 * @note总是在使用解码例程(例如@ref avcodec_receive_frame())之前调用这个函数。
 *
 * @code
 * av_dict_set(&opts, "b", "2.5M", 0);
 * codec = avcodec_find_decoder(AV_CODEC_ID_H264);
 * if (!codec)
 *     exit(1);
 *
 * context = avcodec_alloc_context3(codec);
 *
 * if (avcodec_open2(context, codec, opts) < 0)
 *     exit(1);
 * @endcode
 *
 * @param avctx 要初始化的上下文。
 * @param codec 打开此上下文的编解码器。
 *              如果一个非空的编解码器之前已经传递给avcodec_alloc_context3()或这个上下文，
 *              那么这个参数必须是NULL或等于之前传递的编解码器
 * @param options 一个充满AVCodecContext和codec-private选项的字典。
 *                返回时，该对象将被未找到的选项填充。
 *
 * @return 成功为零，错误为负值
 * @see avcodec_alloc_context3(), avcodec_find_decoder(), avcodec_find_encoder(),
 *      av_dict_set(), av_opt_find().
 */
int avcodec_open2(AVCodecContext *avctx, const AVCodec *codec, AVDictionary **options);

/**
 * 关闭给定的AVCodecContext并释放与其关联的所有数据（但不是AVCodecContext本身）。
 *
 * Calling this function on an AVCodecContext that hasn't been opened will free
 * the codec-specific data allocated in avcodec_alloc_context3() with a non-NULL
 * codec. Subsequent calls will do nothing.
 *
 * @note Do not use this function. Use avcodec_free_context() to destroy a
 * codec context (either open or closed). Opening and closing a codec context
 * multiple times is not supported anymore -- use multiple codec contexts
 * instead.
 */
int avcodec_close(AVCodecContext *avctx);

/**
 * Free all allocated data in the given subtitle struct.
 *
 * @param sub AVSubtitle to free.
 */
void avsubtitle_free(AVSubtitle *sub);

/**
 * @}
 */

/**
 * @addtogroup lavc_decoding
 * @{
 */

/**
 * The default callback for AVCodecContext.get_buffer2(). It is made public so
 * it can be called by custom get_buffer2() implementations for decoders without
 * AV_CODEC_CAP_DR1 set.
 */
int avcodec_default_get_buffer2(AVCodecContext *s, AVFrame *frame, int flags);

/**
 * The default callback for AVCodecContext.get_encode_buffer(). It is made public so
 * it can be called by custom get_encode_buffer() implementations for encoders without
 * AV_CODEC_CAP_DR1 set.
 */
int avcodec_default_get_encode_buffer(AVCodecContext *s, AVPacket *pkt, int flags);

/**
 * Modify width and height values so that they will result in a memory
 * buffer that is acceptable for the codec if you do not use any horizontal
 * padding.
 *
 * May only be used if a codec with AV_CODEC_CAP_DR1 has been opened.
 */
void avcodec_align_dimensions(AVCodecContext *s, int *width, int *height);

/**
 * Modify width and height values so that they will result in a memory
 * buffer that is acceptable for the codec if you also ensure that all
 * line sizes are a multiple of the respective linesize_align[i].
 *
 * May only be used if a codec with AV_CODEC_CAP_DR1 has been opened.
 */
void avcodec_align_dimensions2(AVCodecContext *s, int *width, int *height,
                               int linesize_align[AV_NUM_DATA_POINTERS]);

/**
 * Converts AVChromaLocation to swscale x/y chroma position.
 *
 * The positions represent the chroma (0,0) position in a coordinates system
 * with luma (0,0) representing the origin and luma(1,1) representing 256,256
 *
 * @param xpos  horizontal chroma sample position
 * @param ypos  vertical   chroma sample position
 */
int avcodec_enum_to_chroma_pos(int *xpos, int *ypos, enum AVChromaLocation pos);

/**
 * Converts swscale x/y chroma position to AVChromaLocation.
 *
 * The positions represent the chroma (0,0) position in a coordinates system
 * with luma (0,0) representing the origin and luma(1,1) representing 256,256
 *
 * @param xpos  horizontal chroma sample position
 * @param ypos  vertical   chroma sample position
 */
enum AVChromaLocation avcodec_chroma_pos_to_enum(int xpos, int ypos);

/**
 * Decode a subtitle message.
 * Return a negative value on error, otherwise return the number of bytes used.
 * If no subtitle could be decompressed, got_sub_ptr is zero.
 * Otherwise, the subtitle is stored in *sub.
 * Note that AV_CODEC_CAP_DR1 is not available for subtitle codecs. This is for
 * simplicity, because the performance difference is expected to be negligible
 * and reusing a get_buffer written for video codecs would probably perform badly
 * due to a potentially very different allocation pattern.
 *
 * Some decoders (those marked with AV_CODEC_CAP_DELAY) have a delay between input
 * and output. This means that for some packets they will not immediately
 * produce decoded output and need to be flushed at the end of decoding to get
 * all the decoded data. Flushing is done by calling this function with packets
 * with avpkt->data set to NULL and avpkt->size set to 0 until it stops
 * returning subtitles. It is safe to flush even those decoders that are not
 * marked with AV_CODEC_CAP_DELAY, then no subtitles will be returned.
 *
 * @note The AVCodecContext MUST have been opened with @ref avcodec_open2()
 * before packets may be fed to the decoder.
 *
 * @param avctx the codec context
 * @param[out] sub The preallocated AVSubtitle in which the decoded subtitle will be stored,
 *                 must be freed with avsubtitle_free if *got_sub_ptr is set.
 * @param[in,out] got_sub_ptr Zero if no subtitle could be decompressed, otherwise, it is nonzero.
 * @param[in] avpkt The input AVPacket containing the input buffer.
 */
int avcodec_decode_subtitle2(AVCodecContext *avctx, AVSubtitle *sub,
                            int *got_sub_ptr,
                            AVPacket *avpkt);

/**
 * 提供原始数据包数据作为解码器的输入。
 *
 * 在内部，这个调用将复制相关的AVCodecContext字段，
 * 这些字段可能会影响每个包的解码，并在实际解码包时应用它们。
 * (例如AVCodecContext。Skip_frame，它可能指示解码器丢弃与此函数一起发送的包所包含的帧。)
 *
 * @warning 输入缓冲区avpkt->data必须大于实际读取字节的AV_input_buffer_PADDING_SIZE，
 * 因为一些优化的比特流读取器一次读取32或64位，并且可以从末尾读取。
 *
 * @note AVCodecContext必须用@ref avcodec_open2()打开，然后才能将数据包送入解码器。
 *
 * @param avctx 编解码器上下文
 * @param[in] avpkt 输入AVPacket。通常，这将是一个单一的视频帧，或几个完整的音频帧。
 *                  数据包的所有权仍然属于调用方，解码器不会对数据包进行写操作。
 *                  解码器可以创建对包数据的引用(如果包没有被引用计数，则复制它)。
 *                  与旧的api不同，包总是被完全消耗，如果它包含多个帧(例如一些音频编解码器)，
 *                  将需要你调用avcodec_receive_frame()多次之后，你可以发送一个新的包。
 *                  它可以是NULL(或者数据设置为NULL，大小设置为0的AVPacket);
 *                  在这种情况下，它被认为是一个刷新包，它标志着流的结束。
 *                  发送第一个flush包将返回成功。
 *                  后续的操作是不必要的，将返回AVERROR_EOF。
 *                  如果解码器仍然有帧缓冲，
 *                  它将在发送flush包后返回它们。
 *
 * @return 成功时为0，否则为负错误代码：
 *      AVERROR(EAGAIN):   input is not accepted in the current state - user
 *                         must read output with avcodec_receive_frame() (once
 *                         all output is read, the packet should be resent, and
 *                         the call will not fail with EAGAIN).
 *      AVERROR_EOF:       the decoder has been flushed, and no new packets can
 *                         be sent to it (also returned if more than 1 flush
 *                         packet is sent)
 *      AVERROR(EINVAL):   codec not opened, it is an encoder, or requires flush
 *      AVERROR(ENOMEM):   failed to add packet to internal queue, or similar
 *      other errors: legitimate decoding errors
 */
int avcodec_send_packet(AVCodecContext *avctx, const AVPacket *avpkt);

/**
 * 从解码器返回解码的输出数据。
 *
 * @param avctx 编解码器上下文
 * @param frame 这将设置为解码器分配的参考计数视频或音频帧（取决于解码器类型）。
 *              请注意，在执行其他操作之前，该函数将始终调用av_frame_unref（frame）。
 *
 * @return
 *      0:                 成功，返回一帧
 *      AVERROR(EAGAIN):   output is not available in this state - user must try
 *                         to send new input
 *      AVERROR_EOF:       the decoder has been fully flushed, and there will be
 *                         no more output frames
 *      AVERROR(EINVAL):   codec not opened, or it is an encoder
 *      AVERROR_INPUT_CHANGED:   current decoded frame has changed parameters
 *                               with respect to first decoded frame. Applicable
 *                               when flag AV_CODEC_FLAG_DROPCHANGED is set.
 *      other negative values: legitimate decoding errors
 */
int avcodec_receive_frame(AVCodecContext *avctx, AVFrame *frame);

/**
 * Supply a raw video or audio frame to the encoder. Use avcodec_receive_packet()
 * to retrieve buffered output packets.
 *
 * @param avctx     codec context
 * @param[in] frame AVFrame containing the raw audio or video frame to be encoded.
 *                  Ownership of the frame remains with the caller, and the
 *                  encoder will not write to the frame. The encoder may create
 *                  a reference to the frame data (or copy it if the frame is
 *                  not reference-counted).
 *                  It can be NULL, in which case it is considered a flush
 *                  packet.  This signals the end of the stream. If the encoder
 *                  still has packets buffered, it will return them after this
 *                  call. Once flushing mode has been entered, additional flush
 *                  packets are ignored, and sending frames will return
 *                  AVERROR_EOF.
 *
 *                  For audio:
 *                  If AV_CODEC_CAP_VARIABLE_FRAME_SIZE is set, then each frame
 *                  can have any number of samples.
 *                  If it is not set, frame->nb_samples must be equal to
 *                  avctx->frame_size for all frames except the last.
 *                  The final frame may be smaller than avctx->frame_size.
 * @return 0 on success, otherwise negative error code:
 *      AVERROR(EAGAIN):   input is not accepted in the current state - user
 *                         must read output with avcodec_receive_packet() (once
 *                         all output is read, the packet should be resent, and
 *                         the call will not fail with EAGAIN).
 *      AVERROR_EOF:       the encoder has been flushed, and no new frames can
 *                         be sent to it
 *      AVERROR(EINVAL):   codec not opened, it is a decoder, or requires flush
 *      AVERROR(ENOMEM):   failed to add packet to internal queue, or similar
 *      other errors: legitimate encoding errors
 */
int avcodec_send_frame(AVCodecContext *avctx, const AVFrame *frame);

/**
 * Read encoded data from the encoder.
 *
 * @param avctx codec context
 * @param avpkt This will be set to a reference-counted packet allocated by the
 *              encoder. Note that the function will always call
 *              av_packet_unref(avpkt) before doing anything else.
 * @return 0 on success, otherwise negative error code:
 *      AVERROR(EAGAIN):   output is not available in the current state - user
 *                         must try to send input
 *      AVERROR_EOF:       the encoder has been fully flushed, and there will be
 *                         no more output packets
 *      AVERROR(EINVAL):   codec not opened, or it is a decoder
 *      other errors: legitimate encoding errors
 */
int avcodec_receive_packet(AVCodecContext *avctx, AVPacket *avpkt);

/**
 * Create and return a AVHWFramesContext with values adequate for hardware
 * decoding. This is meant to get called from the get_format callback, and is
 * a helper for preparing a AVHWFramesContext for AVCodecContext.hw_frames_ctx.
 * This API is for decoding with certain hardware acceleration modes/APIs only.
 *
 * The returned AVHWFramesContext is not initialized. The caller must do this
 * with av_hwframe_ctx_init().
 *
 * Calling this function is not a requirement, but makes it simpler to avoid
 * codec or hardware API specific details when manually allocating frames.
 *
 * Alternatively to this, an API user can set AVCodecContext.hw_device_ctx,
 * which sets up AVCodecContext.hw_frames_ctx fully automatically, and makes
 * it unnecessary to call this function or having to care about
 * AVHWFramesContext initialization at all.
 *
 * There are a number of requirements for calling this function:
 *
 * - It must be called from get_format with the same avctx parameter that was
 *   passed to get_format. Calling it outside of get_format is not allowed, and
 *   can trigger undefined behavior.
 * - The function is not always supported (see description of return values).
 *   Even if this function returns successfully, hwaccel initialization could
 *   fail later. (The degree to which implementations check whether the stream
 *   is actually supported varies. Some do this check only after the user's
 *   get_format callback returns.)
 * - The hw_pix_fmt must be one of the choices suggested by get_format. If the
 *   user decides to use a AVHWFramesContext prepared with this API function,
 *   the user must return the same hw_pix_fmt from get_format.
 * - The device_ref passed to this function must support the given hw_pix_fmt.
 * - After calling this API function, it is the user's responsibility to
 *   initialize the AVHWFramesContext (returned by the out_frames_ref parameter),
 *   and to set AVCodecContext.hw_frames_ctx to it. If done, this must be done
 *   before returning from get_format (this is implied by the normal
 *   AVCodecContext.hw_frames_ctx API rules).
 * - The AVHWFramesContext parameters may change every time time get_format is
 *   called. Also, AVCodecContext.hw_frames_ctx is reset before get_format. So
 *   you are inherently required to go through this process again on every
 *   get_format call.
 * - It is perfectly possible to call this function without actually using
 *   the resulting AVHWFramesContext. One use-case might be trying to reuse a
 *   previously initialized AVHWFramesContext, and calling this API function
 *   only to test whether the required frame parameters have changed.
 * - Fields that use dynamically allocated values of any kind must not be set
 *   by the user unless setting them is explicitly allowed by the documentation.
 *   If the user sets AVHWFramesContext.free and AVHWFramesContext.user_opaque,
 *   the new free callback must call the potentially set previous free callback.
 *   This API call may set any dynamically allocated fields, including the free
 *   callback.
 *
 * The function will set at least the following fields on AVHWFramesContext
 * (potentially more, depending on hwaccel API):
 *
 * - All fields set by av_hwframe_ctx_alloc().
 * - Set the format field to hw_pix_fmt.
 * - Set the sw_format field to the most suited and most versatile format. (An
 *   implication is that this will prefer generic formats over opaque formats
 *   with arbitrary restrictions, if possible.)
 * - Set the width/height fields to the coded frame size, rounded up to the
 *   API-specific minimum alignment.
 * - Only _if_ the hwaccel requires a pre-allocated pool: set the initial_pool_size
 *   field to the number of maximum reference surfaces possible with the codec,
 *   plus 1 surface for the user to work (meaning the user can safely reference
 *   at most 1 decoded surface at a time), plus additional buffering introduced
 *   by frame threading. If the hwaccel does not require pre-allocation, the
 *   field is left to 0, and the decoder will allocate new surfaces on demand
 *   during decoding.
 * - Possibly AVHWFramesContext.hwctx fields, depending on the underlying
 *   hardware API.
 *
 * Essentially, out_frames_ref returns the same as av_hwframe_ctx_alloc(), but
 * with basic frame parameters set.
 *
 * The function is stateless, and does not change the AVCodecContext or the
 * device_ref AVHWDeviceContext.
 *
 * @param avctx The context which is currently calling get_format, and which
 *              implicitly contains all state needed for filling the returned
 *              AVHWFramesContext properly.
 * @param device_ref A reference to the AVHWDeviceContext describing the device
 *                   which will be used by the hardware decoder.
 * @param hw_pix_fmt The hwaccel format you are going to return from get_format.
 * @param out_frames_ref On success, set to a reference to an _uninitialized_
 *                       AVHWFramesContext, created from the given device_ref.
 *                       Fields will be set to values required for decoding.
 *                       Not changed if an error is returned.
 * @return zero on success, a negative value on error. The following error codes
 *         have special semantics:
 *      AVERROR(ENOENT): the decoder does not support this functionality. Setup
 *                       is always manual, or it is a decoder which does not
 *                       support setting AVCodecContext.hw_frames_ctx at all,
 *                       or it is a software format.
 *      AVERROR(EINVAL): it is known that hardware decoding is not supported for
 *                       this configuration, or the device_ref is not supported
 *                       for the hwaccel referenced by hw_pix_fmt.
 */
int avcodec_get_hw_frames_parameters(AVCodecContext *avctx,
                                     AVBufferRef *device_ref,
                                     enum AVPixelFormat hw_pix_fmt,
                                     AVBufferRef **out_frames_ref);



/**
 * @defgroup lavc_parsing Frame parsing
 * @{
 */

enum AVPictureStructure {
    AV_PICTURE_STRUCTURE_UNKNOWN,      //< unknown
    AV_PICTURE_STRUCTURE_TOP_FIELD,    //< coded as top field
    AV_PICTURE_STRUCTURE_BOTTOM_FIELD, //< coded as bottom field
    AV_PICTURE_STRUCTURE_FRAME,        //< coded as frame
};

typedef struct AVCodecParserContext {
    void *priv_data;
    const struct AVCodecParser *parser;
    int64_t frame_offset; /* offset of the current frame */
    int64_t cur_offset; /* current offset
                           (incremented by each av_parser_parse()) */
    int64_t next_frame_offset; /* offset of the next frame */
    /* video info */
    int pict_type; /* XXX: Put it back in AVCodecContext. */
    /**
     * This field is used for proper frame duration computation in lavf.
     * It signals, how much longer the frame duration of the current frame
     * is compared to normal frame duration.
     *
     * frame_duration = (1 + repeat_pict) * time_base
     *
     * It is used by codecs like H.264 to display telecined material.
     */
    int repeat_pict; /* XXX: Put it back in AVCodecContext. */
    int64_t pts;     /* pts of the current frame */
    int64_t dts;     /* dts of the current frame */

    /* private data */
    int64_t last_pts;
    int64_t last_dts;
    int fetch_timestamp;

#define AV_PARSER_PTS_NB 4
    int cur_frame_start_index;
    int64_t cur_frame_offset[AV_PARSER_PTS_NB];
    int64_t cur_frame_pts[AV_PARSER_PTS_NB];
    int64_t cur_frame_dts[AV_PARSER_PTS_NB];

    int flags;
#define PARSER_FLAG_COMPLETE_FRAMES           0x0001
#define PARSER_FLAG_ONCE                      0x0002
/// Set if the parser has a valid file offset
#define PARSER_FLAG_FETCHED_OFFSET            0x0004
#define PARSER_FLAG_USE_CODEC_TS              0x1000

    int64_t offset;      ///< byte offset from starting packet start
    int64_t cur_frame_end[AV_PARSER_PTS_NB];

    /**
     * Set by parser to 1 for key frames and 0 for non-key frames.
     * It is initialized to -1, so if the parser doesn't set this flag,
     * old-style fallback using AV_PICTURE_TYPE_I picture type as key frames
     * will be used.
     */
    int key_frame;

    // Timestamp generation support:
    /**
     * Synchronization point for start of timestamp generation.
     *
     * Set to >0 for sync point, 0 for no sync point and <0 for undefined
     * (default).
     *
     * For example, this corresponds to presence of H.264 buffering period
     * SEI message.
     */
    int dts_sync_point;

    /**
     * Offset of the current timestamp against last timestamp sync point in
     * units of AVCodecContext.time_base.
     *
     * Set to INT_MIN when dts_sync_point unused. Otherwise, it must
     * contain a valid timestamp offset.
     *
     * Note that the timestamp of sync point has usually a nonzero
     * dts_ref_dts_delta, which refers to the previous sync point. Offset of
     * the next frame after timestamp sync point will be usually 1.
     *
     * For example, this corresponds to H.264 cpb_removal_delay.
     */
    int dts_ref_dts_delta;

    /**
     * Presentation delay of current frame in units of AVCodecContext.time_base.
     *
     * Set to INT_MIN when dts_sync_point unused. Otherwise, it must
     * contain valid non-negative timestamp delta (presentation time of a frame
     * must not lie in the past).
     *
     * This delay represents the difference between decoding and presentation
     * time of the frame.
     *
     * For example, this corresponds to H.264 dpb_output_delay.
     */
    int pts_dts_delta;

    /**
     * Position of the packet in file.
     *
     * Analogous to cur_frame_pts/dts
     */
    int64_t cur_frame_pos[AV_PARSER_PTS_NB];

    /**
     * Byte position of currently parsed frame in stream.
     */
    int64_t pos;

    /**
     * Previous frame byte position.
     */
    int64_t last_pos;

    /**
     * Duration of the current frame.
     * For audio, this is in units of 1 / AVCodecContext.sample_rate.
     * For all other types, this is in units of AVCodecContext.time_base.
     */
    int duration;

    enum AVFieldOrder field_order;

    /**
     * Indicate whether a picture is coded as a frame, top field or bottom field.
     *
     * For example, H.264 field_pic_flag equal to 0 corresponds to
     * AV_PICTURE_STRUCTURE_FRAME. An H.264 picture with field_pic_flag
     * equal to 1 and bottom_field_flag equal to 0 corresponds to
     * AV_PICTURE_STRUCTURE_TOP_FIELD.
     */
    enum AVPictureStructure picture_structure;

    /**
     * Picture number incremented in presentation or output order.
     * This field may be reinitialized at the first picture of a new sequence.
     *
     * For example, this corresponds to H.264 PicOrderCnt.
     */
    int output_picture_number;

    /**
     * Dimensions of the decoded video intended for presentation.
     */
    int width;
    int height;

    /**
     * Dimensions of the coded video.
     */
    int coded_width;
    int coded_height;

    /**
     * The format of the coded data, corresponds to enum AVPixelFormat for video
     * and for enum AVSampleFormat for audio.
     *
     * Note that a decoder can have considerable freedom in how exactly it
     * decodes the data, so the format reported here might be different from the
     * one returned by a decoder.
     */
    int format;
} AVCodecParserContext;

typedef struct AVCodecParser {
    int codec_ids[7]; /* several codec IDs are permitted */
    int priv_data_size;
    int (*parser_init)(AVCodecParserContext *s);
    /* This callback never returns an error, a negative value means that
     * the frame start was in a previous packet. */
    int (*parser_parse)(AVCodecParserContext *s,
                        AVCodecContext *avctx,
                        const uint8_t **poutbuf, int *poutbuf_size,
                        const uint8_t *buf, int buf_size);
    void (*parser_close)(AVCodecParserContext *s);
    int (*split)(AVCodecContext *avctx, const uint8_t *buf, int buf_size);
} AVCodecParser;

/**
 * Iterate over all registered codec parsers.
 *
 * @param opaque a pointer where libavcodec will store the iteration state. Must
 *               point to NULL to start the iteration.
 *
 * @return the next registered codec parser or NULL when the iteration is
 *         finished
 */
const AVCodecParser *av_parser_iterate(void **opaque);

AVCodecParserContext *av_parser_init(int codec_id);

/**
 * Parse a packet.
 *
 * @param s             parser context.
 * @param avctx         codec context.
 * @param poutbuf       set to pointer to parsed buffer or NULL if not yet finished.
 * @param poutbuf_size  set to size of parsed buffer or zero if not yet finished.
 * @param buf           input buffer.
 * @param buf_size      buffer size in bytes without the padding. I.e. the full buffer
                        size is assumed to be buf_size + AV_INPUT_BUFFER_PADDING_SIZE.
                        To signal EOF, this should be 0 (so that the last frame
                        can be output).
 * @param pts           input presentation timestamp.
 * @param dts           input decoding timestamp.
 * @param pos           input byte position in stream.
 * @return the number of bytes of the input bitstream used.
 *
 * Example:
 * @code
 *   while(in_len){
 *       len = av_parser_parse2(myparser, AVCodecContext, &data, &size,
 *                                        in_data, in_len,
 *                                        pts, dts, pos);
 *       in_data += len;
 *       in_len  -= len;
 *
 *       if(size)
 *          decode_frame(data, size);
 *   }
 * @endcode
 */
int av_parser_parse2(AVCodecParserContext *s,
                     AVCodecContext *avctx,
                     uint8_t **poutbuf, int *poutbuf_size,
                     const uint8_t *buf, int buf_size,
                     int64_t pts, int64_t dts,
                     int64_t pos);

void av_parser_close(AVCodecParserContext *s);

/**
 * @}
 * @}
 */

/**
 * @addtogroup lavc_encoding
 * @{
 */

int avcodec_encode_subtitle(AVCodecContext *avctx, uint8_t *buf, int buf_size,
                            const AVSubtitle *sub);


/**
 * @}
 */

/**
 * @defgroup lavc_misc Utility functions
 * @ingroup libavc
 *
 * Miscellaneous utility functions related to both encoding and decoding
 * (or neither).
 * @{
 */

/**
 * @defgroup lavc_misc_pixfmt Pixel formats
 *
 * Functions for working with pixel formats.
 * @{
 */

/**
 * Return a value representing the fourCC code associated to the
 * pixel format pix_fmt, or 0 if no associated fourCC code can be
 * found.
 */
unsigned int avcodec_pix_fmt_to_codec_tag(enum AVPixelFormat pix_fmt);

/**
 * Find the best pixel format to convert to given a certain source pixel
 * format.  When converting from one pixel format to another, information loss
 * may occur.  For example, when converting from RGB24 to GRAY, the color
 * information will be lost. Similarly, other losses occur when converting from
 * some formats to other formats. avcodec_find_best_pix_fmt_of_2() searches which of
 * the given pixel formats should be used to suffer the least amount of loss.
 * The pixel formats from which it chooses one, are determined by the
 * pix_fmt_list parameter.
 *
 *
 * @param[in] pix_fmt_list AV_PIX_FMT_NONE terminated array of pixel formats to choose from
 * @param[in] src_pix_fmt source pixel format
 * @param[in] has_alpha Whether the source pixel format alpha channel is used.
 * @param[out] loss_ptr Combination of flags informing you what kind of losses will occur.
 * @return The best pixel format to convert to or -1 if none was found.
 */
enum AVPixelFormat avcodec_find_best_pix_fmt_of_list(const enum AVPixelFormat *pix_fmt_list,
                                            enum AVPixelFormat src_pix_fmt,
                                            int has_alpha, int *loss_ptr);

enum AVPixelFormat avcodec_default_get_format(struct AVCodecContext *s, const enum AVPixelFormat * fmt);

/**
 * @}
 */

void avcodec_string(char *buf, int buf_size, AVCodecContext *enc, int encode);

int avcodec_default_execute(AVCodecContext *c, int (*func)(AVCodecContext *c2, void *arg2),void *arg, int *ret, int count, int size);
int avcodec_default_execute2(AVCodecContext *c, int (*func)(AVCodecContext *c2, void *arg2, int, int),void *arg, int *ret, int count);
//FIXME func typedef

/**
 * Fill AVFrame audio data and linesize pointers.
 *
 * The buffer buf must be a preallocated buffer with a size big enough
 * to contain the specified samples amount. The filled AVFrame data
 * pointers will point to this buffer.
 *
 * AVFrame extended_data channel pointers are allocated if necessary for
 * planar audio.
 *
 * @param frame       the AVFrame
 *                    frame->nb_samples must be set prior to calling the
 *                    function. This function fills in frame->data,
 *                    frame->extended_data, frame->linesize[0].
 * @param nb_channels channel count
 * @param sample_fmt  sample format
 * @param buf         buffer to use for frame data
 * @param buf_size    size of buffer
 * @param align       plane size sample alignment (0 = default)
 * @return            >=0 on success, negative error code on failure
 * @todo return the size in bytes required to store the samples in
 * case of success, at the next libavutil bump
 */
int avcodec_fill_audio_frame(AVFrame *frame, int nb_channels,
                             enum AVSampleFormat sample_fmt, const uint8_t *buf,
                             int buf_size, int align);

/**
 * Reset the internal codec state / flush internal buffers. Should be called
 * e.g. when seeking or when switching to a different stream.
 *
 * @note for decoders, this function just releases any references the decoder
 * might keep internally, but the caller's references remain valid.
 *
 * @note for encoders, this function will only do something if the encoder
 * declares support for AV_CODEC_CAP_ENCODER_FLUSH. When called, the encoder
 * will drain any remaining packets, and can then be re-used for a different
 * stream (as opposed to sending a null frame which will leave the encoder
 * in a permanent EOF state after draining). This can be desirable if the
 * cost of tearing down and replacing the encoder instance is high.
 */
void avcodec_flush_buffers(AVCodecContext *avctx);

/**
 * Return audio frame duration.
 *
 * @param avctx        codec context
 * @param frame_bytes  size of the frame, or 0 if unknown
 * @return             frame duration, in samples, if known. 0 if not able to
 *                     determine.
 */
int av_get_audio_frame_duration(AVCodecContext *avctx, int frame_bytes);

/* memory */

/**
 * Same behaviour av_fast_malloc but the buffer has additional
 * AV_INPUT_BUFFER_PADDING_SIZE at the end which will always be 0.
 *
 * In addition the whole buffer will initially and after resizes
 * be 0-initialized so that no uninitialized data will ever appear.
 */
void av_fast_padded_malloc(void *ptr, unsigned int *size, size_t min_size);

/**
 * Same behaviour av_fast_padded_malloc except that buffer will always
 * be 0-initialized after call.
 */
void av_fast_padded_mallocz(void *ptr, unsigned int *size, size_t min_size);

/**
 * @return a positive value if s is open (i.e. avcodec_open2() was called on it
 * with no corresponding avcodec_close()), 0 otherwise.
 */
int avcodec_is_open(AVCodecContext *s);

/**
 * @}
 */

#endif /* AVCODEC_AVCODEC_H */