ffmpeg 关键数据结构

ffmpeg 关键数据结构

AVFormatContext

libavformat/avformat.h

/**
 * Format I/O context.
 * New fields can be added to the end with minor version bumps.
 * Removal, reordering and changes to existing fields require a major
 * version bump.
 * sizeof(AVFormatContext) must not be used outside libav*, use
 * avformat_alloc_context() to create an AVFormatContext.
 *
 * Fields can be accessed through AVOptions (av_opt*),
 * the name string used matches the associated command line parameter name and
 * can be found in libavformat/options_table.h.
 * The AVOption/command line parameter names differ in some cases from the C
 * structure field names for historic reasons or brevity.
 */
typedef struct AVFormatContext {
    /**
     * A class for logging and @ref avoptions. Set by avformat_alloc_context().
     * Exports (de)muxer private options if they exist.
     */
    const AVClass *av_class;

    /**
     * The input container format.
     *
     * Demuxing only, set by avformat_open_input().
     */
    ff_const59 struct AVInputFormat *iformat;

    /**
     * The output container format.
     *
     * Muxing only, must be set by the caller before avformat_write_header().
     */
    ff_const59 struct AVOutputFormat *oformat;

    /**
     * Format private data. This is an AVOptions-enabled struct
     * if and only if iformat/oformat.priv_class is not NULL.
     *
     * - muxing: set by avformat_write_header()
     * - demuxing: set by avformat_open_input()
     */
    void *priv_data;

    /**
     * I/O context.
     *
     * - demuxing: either set by the user before avformat_open_input() (then
     *             the user must close it manually) or set by avformat_open_input().
     * - muxing: set by the user before avformat_write_header(). The caller must
     *           take care of closing / freeing the IO context.
     *
     * Do NOT set this field if AVFMT_NOFILE flag is set in
     * iformat/oformat.flags. In such a case, the (de)muxer will handle
     * I/O in some other way and this field will be NULL.
     */
    AVIOContext *pb;

    /* stream info */
    /**
     * Flags signalling stream properties. A combination of AVFMTCTX_*.
     * Set by libavformat.
     */
    int ctx_flags;

    /**
     * Number of elements in AVFormatContext.streams.
     *
     * Set by avformat_new_stream(), must not be modified by any other code.
     */
    unsigned int nb_streams;
    /**
     * A list of all streams in the file. New streams are created with
     * avformat_new_stream().
     *
     * - demuxing: streams are created by libavformat in avformat_open_input().
     *             If AVFMTCTX_NOHEADER is set in ctx_flags, then new streams may also
     *             appear in av_read_frame().
     * - muxing: streams are created by the user before avformat_write_header().
     *
     * Freed by libavformat in avformat_free_context().
     */
    AVStream **streams;

#if FF_API_FORMAT_FILENAME
    /**
     * input or output filename
     *
     * - demuxing: set by avformat_open_input()
     * - muxing: may be set by the caller before avformat_write_header()
     *
     * @deprecated Use url instead.
     */
    attribute_deprecated
    char filename[1024];
#endif

    /**
     * input or output URL. Unlike the old filename field, this field has no
     * length restriction.
     *
     * - demuxing: set by avformat_open_input(), initialized to an empty
     *             string if url parameter was NULL in avformat_open_input().
     * - muxing: may be set by the caller before calling avformat_write_header()
     *           (or avformat_init_output() if that is called first) to a string
     *           which is freeable by av_free(). Set to an empty string if it
     *           was NULL in avformat_init_output().
     *
     * Freed by libavformat in avformat_free_context().
     */
    char *url;

    /**
     * Position of the first frame of the component, in
     * AV_TIME_BASE fractional seconds. NEVER set this value directly:
     * It is deduced from the AVStream values.
     *
     * Demuxing only, set by libavformat.
     */
    int64_t start_time;

    /**
     * Duration of the stream, in AV_TIME_BASE fractional
     * seconds. Only set this value if you know none of the individual stream
     * durations and also do not set any of them. This is deduced from the
     * AVStream values if not set.
     *
     * Demuxing only, set by libavformat.
     */
    int64_t duration;

    /**
     * Total stream bitrate in bit/s, 0 if not
     * available. Never set it directly if the file_size and the
     * duration are known as FFmpeg can compute it automatically.
     */
    int64_t bit_rate;

    unsigned int packet_size;
    int max_delay;

    /**
     * Flags modifying the (de)muxer behaviour. A combination of AVFMT_FLAG_*.
     * Set by the user before avformat_open_input() / avformat_write_header().
     */
    int flags;
#define AVFMT_FLAG_GENPTS       0x0001 ///< Generate missing pts even if it requires parsing future frames.
#define AVFMT_FLAG_IGNIDX       0x0002 ///< Ignore index.
#define AVFMT_FLAG_NONBLOCK     0x0004 ///< Do not block when reading packets from input.
#define AVFMT_FLAG_IGNDTS       0x0008 ///< Ignore DTS on frames that contain both DTS & PTS
#define AVFMT_FLAG_NOFILLIN     0x0010 ///< Do not infer any values from other values, just return what is stored in the container
#define AVFMT_FLAG_NOPARSE      0x0020 ///< Do not use AVParsers, you also must set AVFMT_FLAG_NOFILLIN as the fillin code works on frames and no parsing -> no frames. Also seeking to frames can not work if parsing to find frame boundaries has been disabled
#define AVFMT_FLAG_NOBUFFER     0x0040 ///< Do not buffer frames when possible
#define AVFMT_FLAG_CUSTOM_IO    0x0080 ///< The caller has supplied a custom AVIOContext, don't avio_close() it.
#define AVFMT_FLAG_DISCARD_CORRUPT  0x0100 ///< Discard frames marked corrupted
#define AVFMT_FLAG_FLUSH_PACKETS    0x0200 ///< Flush the AVIOContext every packet.
/**
 * When muxing, try to avoid writing any random/volatile data to the output.
 * This includes any random IDs, real-time timestamps/dates, muxer version, etc.
 *
 * This flag is mainly intended for testing.
 */
#define AVFMT_FLAG_BITEXACT         0x0400
#if FF_API_LAVF_MP4A_LATM
#define AVFMT_FLAG_MP4A_LATM    0x8000 ///< Deprecated, does nothing.
#endif
#define AVFMT_FLAG_SORT_DTS    0x10000 ///< try to interleave outputted packets by dts (using this flag can slow demuxing down)
#define AVFMT_FLAG_PRIV_OPT    0x20000 ///< Enable use of private options by delaying codec open (this could be made default once all code is converted)
#if FF_API_LAVF_KEEPSIDE_FLAG
#define AVFMT_FLAG_KEEP_SIDE_DATA 0x40000 ///< Deprecated, does nothing.
#endif
#define AVFMT_FLAG_FAST_SEEK   0x80000 ///< Enable fast, but inaccurate seeks for some formats
#define AVFMT_FLAG_SHORTEST   0x100000 ///< Stop muxing when the shortest stream stops.
#define AVFMT_FLAG_AUTO_BSF   0x200000 ///< Add bitstream filters as requested by the muxer

    /**
     * Maximum size of the data read from input for determining
     * the input container format.
     * Demuxing only, set by the caller before avformat_open_input().
     */
    int64_t probesize;

    /**
     * Maximum duration (in AV_TIME_BASE units) of the data read
     * from input in avformat_find_stream_info().
     * Demuxing only, set by the caller before avformat_find_stream_info().
     * Can be set to 0 to let avformat choose using a heuristic.
     */
    int64_t max_analyze_duration;

    const uint8_t *key;
    int keylen;

    unsigned int nb_programs;
    AVProgram **programs;

    /**
     * Forced video codec_id.
     * Demuxing: Set by user.
     */
    enum AVCodecID video_codec_id;

    /**
     * Forced audio codec_id.
     * Demuxing: Set by user.
     */
    enum AVCodecID audio_codec_id;

    /**
     * Forced subtitle codec_id.
     * Demuxing: Set by user.
     */
    enum AVCodecID subtitle_codec_id;

    /**
     * Maximum amount of memory in bytes to use for the index of each stream.
     * If the index exceeds this size, entries will be discarded as
     * needed to maintain a smaller size. This can lead to slower or less
     * accurate seeking (depends on demuxer).
     * Demuxers for which a full in-memory index is mandatory will ignore
     * this.
     * - muxing: unused
     * - demuxing: set by user
     */
    unsigned int max_index_size;

    /**
     * Maximum amount of memory in bytes to use for buffering frames
     * obtained from realtime capture devices.
     */
    unsigned int max_picture_buffer;

    /**
     * Number of chapters in AVChapter array.
     * When muxing, chapters are normally written in the file header,
     * so nb_chapters should normally be initialized before write_header
     * is called. Some muxers (e.g. mov and mkv) can also write chapters
     * in the trailer.  To write chapters in the trailer, nb_chapters
     * must be zero when write_header is called and non-zero when
     * write_trailer is called.
     * - muxing: set by user
     * - demuxing: set by libavformat
     */
    unsigned int nb_chapters;
    AVChapter **chapters;

    /**
     * Metadata that applies to the whole file.
     *
     * - demuxing: set by libavformat in avformat_open_input()
     * - muxing: may be set by the caller before avformat_write_header()
     *
     * Freed by libavformat in avformat_free_context().
     */
    AVDictionary *metadata;

    /**
     * Start time of the stream in real world time, in microseconds
     * since the Unix epoch (00:00 1st January 1970). That is, pts=0 in the
     * stream was captured at this real world time.
     * - muxing: Set by the caller before avformat_write_header(). If set to
     *           either 0 or AV_NOPTS_VALUE, then the current wall-time will
     *           be used.
     * - demuxing: Set by libavformat. AV_NOPTS_VALUE if unknown. Note that
     *             the value may become known after some number of frames
     *             have been received.
     */
    int64_t start_time_realtime;

    /**
     * The number of frames used for determining the framerate in
     * avformat_find_stream_info().
     * Demuxing only, set by the caller before avformat_find_stream_info().
     */
    int fps_probe_size;

    /**
     * Error recognition; higher values will detect more errors but may
     * misdetect some more or less valid parts as errors.
     * Demuxing only, set by the caller before avformat_open_input().
     */
    int error_recognition;

    /**
     * Custom interrupt callbacks for the I/O layer.
     *
     * demuxing: set by the user before avformat_open_input().
     * muxing: set by the user before avformat_write_header()
     * (mainly useful for AVFMT_NOFILE formats). The callback
     * should also be passed to avio_open2() if it's used to
     * open the file.
     */
    AVIOInterruptCB interrupt_callback;

    /**
     * Flags to enable debugging.
     */
    int debug;
#define FF_FDEBUG_TS        0x0001

    /**
     * Maximum buffering duration for interleaving.
     *
     * To ensure all the streams are interleaved correctly,
     * av_interleaved_write_frame() will wait until it has at least one packet
     * for each stream before actually writing any packets to the output file.
     * When some streams are "sparse" (i.e. there are large gaps between
     * successive packets), this can result in excessive buffering.
     *
     * This field specifies the maximum difference between the timestamps of the
     * first and the last packet in the muxing queue, above which libavformat
     * will output a packet regardless of whether it has queued a packet for all
     * the streams.
     *
     * Muxing only, set by the caller before avformat_write_header().
     */
    int64_t max_interleave_delta;

    /**
     * Allow non-standard and experimental extension
     * @see AVCodecContext.strict_std_compliance
     */
    int strict_std_compliance;

    /**
     * Flags for the user to detect events happening on the file. Flags must
     * be cleared by the user once the event has been handled.
     * A combination of AVFMT_EVENT_FLAG_*.
     */
    int event_flags;
#define AVFMT_EVENT_FLAG_METADATA_UPDATED 0x0001 ///< The call resulted in updated metadata.

    /**
     * Maximum number of packets to read while waiting for the first timestamp.
     * Decoding only.
     */
    int max_ts_probe;

    /**
     * Avoid negative timestamps during muxing.
     * Any value of the AVFMT_AVOID_NEG_TS_* constants.
     * Note, this only works when using av_interleaved_write_frame. (interleave_packet_per_dts is in use)
     * - muxing: Set by user
     * - demuxing: unused
     */
    int avoid_negative_ts;
#define AVFMT_AVOID_NEG_TS_AUTO             -1 ///< Enabled when required by target format
#define AVFMT_AVOID_NEG_TS_MAKE_NON_NEGATIVE 1 ///< Shift timestamps so they are non negative
#define AVFMT_AVOID_NEG_TS_MAKE_ZERO         2 ///< Shift timestamps so that they start at 0

    /**
     * Transport stream id.
     * This will be moved into demuxer private options. Thus no API/ABI compatibility
     */
    int ts_id;

    /**
     * Audio preload in microseconds.
     * Note, not all formats support this and unpredictable things may happen if it is used when not supported.
     * - encoding: Set by user
     * - decoding: unused
     */
    int audio_preload;

    /**
     * Max chunk time in microseconds.
     * Note, not all formats support this and unpredictable things may happen if it is used when not supported.
     * - encoding: Set by user
     * - decoding: unused
     */
    int max_chunk_duration;

    /**
     * Max chunk size in bytes
     * Note, not all formats support this and unpredictable things may happen if it is used when not supported.
     * - encoding: Set by user
     * - decoding: unused
     */
    int max_chunk_size;

    /**
     * forces the use of wallclock timestamps as pts/dts of packets
     * This has undefined results in the presence of B frames.
     * - encoding: unused
     * - decoding: Set by user
     */
    int use_wallclock_as_timestamps;

    /**
     * avio flags, used to force AVIO_FLAG_DIRECT.
     * - encoding: unused
     * - decoding: Set by user
     */
    int avio_flags;

    /**
     * The duration field can be estimated through various ways, and this field can be used
     * to know how the duration was estimated.
     * - encoding: unused
     * - decoding: Read by user
     */
    enum AVDurationEstimationMethod duration_estimation_method;

    /**
     * Skip initial bytes when opening stream
     * - encoding: unused
     * - decoding: Set by user
     */
    int64_t skip_initial_bytes;

    /**
     * Correct single timestamp overflows
     * - encoding: unused
     * - decoding: Set by user
     */
    unsigned int correct_ts_overflow;

    /**
     * Force seeking to any (also non key) frames.
     * - encoding: unused
     * - decoding: Set by user
     */
    int seek2any;

    /**
     * Flush the I/O context after each packet.
     * - encoding: Set by user
     * - decoding: unused
     */
    int flush_packets;

    /**
     * format probing score.
     * The maximal score is AVPROBE_SCORE_MAX, its set when the demuxer probes
     * the format.
     * - encoding: unused
     * - decoding: set by avformat, read by user
     */
    int probe_score;

    /**
     * number of bytes to read maximally to identify format.
     * - encoding: unused
     * - decoding: set by user
     */
    int format_probesize;

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

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

    /**
     * An opaque field for libavformat internal usage.
     * Must not be accessed in any way by callers.
     */
    AVFormatInternal *internal;

    /**
     * IO repositioned flag.
     * This is set by avformat when the underlaying IO context read pointer
     * is repositioned, for example when doing byte based seeking.
     * Demuxers can use the flag to detect such changes.
     */
    int io_repositioned;

    /**
     * Forced video codec.
     * This allows forcing a specific decoder, even when there are multiple with
     * the same codec_id.
     * Demuxing: Set by user
     */
    AVCodec *video_codec;

    /**
     * Forced audio codec.
     * This allows forcing a specific decoder, even when there are multiple with
     * the same codec_id.
     * Demuxing: Set by user
     */
    AVCodec *audio_codec;

    /**
     * Forced subtitle codec.
     * This allows forcing a specific decoder, even when there are multiple with
     * the same codec_id.
     * Demuxing: Set by user
     */
    AVCodec *subtitle_codec;

    /**
     * Forced data codec.
     * This allows forcing a specific decoder, even when there are multiple with
     * the same codec_id.
     * Demuxing: Set by user
     */
    AVCodec *data_codec;

    /**
     * Number of bytes to be written as padding in a metadata header.
     * Demuxing: Unused.
     * Muxing: Set by user via av_format_set_metadata_header_padding.
     */
    int metadata_header_padding;

    /**
     * User data.
     * This is a place for some private data of the user.
     */
    void *opaque;

    /**
     * Callback used by devices to communicate with application.
     */
    av_format_control_message control_message_cb;

    /**
     * Output timestamp offset, in microseconds.
     * Muxing: set by user
     */
    int64_t output_ts_offset;

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

    /**
     * Forced Data codec_id.
     * Demuxing: Set by user.
     */
    enum AVCodecID data_codec_id;

#if FF_API_OLD_OPEN_CALLBACKS
    /**
     * Called to open further IO contexts when needed for demuxing.
     *
     * This can be set by the user application to perform security checks on
     * the URLs before opening them.
     * The function should behave like avio_open2(), AVFormatContext is provided
     * as contextual information and to reach AVFormatContext.opaque.
     *
     * If NULL then some simple checks are used together with avio_open2().
     *
     * Must not be accessed directly from outside avformat.
     * @See av_format_set_open_cb()
     *
     * Demuxing: Set by user.
     *
     * @deprecated Use io_open and io_close.
     */
    attribute_deprecated
    int (*open_cb)(struct AVFormatContext *s, AVIOContext **p, const char *url, int flags, const AVIOInterruptCB *int_cb, AVDictionary **options);
#endif

    /**
     * ',' separated list of allowed protocols.
     * - encoding: unused
     * - decoding: set by user
     */
    char *protocol_whitelist;

    /**
     * A callback for opening new IO streams.
     *
     * Whenever a muxer or a demuxer needs to open an IO stream (typically from
     * avformat_open_input() for demuxers, but for certain formats can happen at
     * other times as well), it will call this callback to obtain an IO context.
     *
     * @param s the format context
     * @param pb on success, the newly opened IO context should be returned here
     * @param url the url to open
     * @param flags a combination of AVIO_FLAG_*
     * @param options a dictionary of additional options, with the same
     *                semantics as in avio_open2()
     * @return 0 on success, a negative AVERROR code on failure
     *
     * @note Certain muxers and demuxers do nesting, i.e. they open one or more
     * additional internal format contexts. Thus the AVFormatContext pointer
     * passed to this callback may be different from the one facing the caller.
     * It will, however, have the same 'opaque' field.
     */
    int (*io_open)(struct AVFormatContext *s, AVIOContext **pb, const char *url,
                   int flags, AVDictionary **options);

    /**
     * A callback for closing the streams opened with AVFormatContext.io_open().
     */
    void (*io_close)(struct AVFormatContext *s, AVIOContext *pb);

    /**
     * ',' separated list of disallowed protocols.
     * - encoding: unused
     * - decoding: set by user
     */
    char *protocol_blacklist;

    /**
     * The maximum number of streams.
     * - encoding: unused
     * - decoding: set by user
     */
    int max_streams;

    /**
     * Skip duration calcuation in estimate_timings_from_pts.
     * - encoding: unused
     * - decoding: set by user
     */
    int skip_estimate_duration_from_pts;
} AVFormatContext;

AVDictionary

libavutil/dict.h

struct AVDictionary {
    int count;
    AVDictionaryEntry *elems;
};
typedef struct AVDictionaryEntry {
    char *key;
    char *value;
} AVDictionaryEntry;

AVDictionary 的elems指针指向AVDictionaryEntry的数组,count是数组中元素的数量。每一个entry是一个key value对。

#include 
#include 
#include 

int main(int argc, char *argv[])
{
    AVDictionary *d = NULL;
    AVDictionaryEntry *entry = NULL;
    char *key = "hello";
    int64_t value = 1000;

    av_log_set_level(AV_LOG_DEBUG);
    av_dict_set_int(&d, key, value, 0);
    av_dict_set(&d, "good", "night", 0);

    while (entry = av_dict_get(d, "", entry, AV_DICT_IGNORE_SUFFIX)) {
        av_log(NULL, AV_LOG_INFO, "key: %s, value: %s\n",
                    entry->key, entry->value);
    }

    av_dict_free(&d);
    return 0;
}

AVCodecContext

/**
 * 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_decode_video2 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;

    /**
     * Pixel format, see AV_PIX_FMT_xxx.
     * May be set by the demuxer if known from headers.
     * May be overridden by the decoder if it knows better.
     *
     * @note This field may not match the value of the last
     * AVFrame output by avcodec_receive_frame() due frame
     * reordering.
     *
     * - 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);

    /**
     * callback to negotiate the pixelFormat
     * @param fmt is the list of formats which are supported by the codec,
     * it is terminated by -1 as 0 is a valid format, the formats are ordered by quality.
     * The first is always the native one.
     * @note The callback may be called again immediately if initialization for
     * the selected (hardware-accelerated) pixel format failed.
     * @warning Behavior is undefined if the callback returns a value not
     * in the fmt list of formats.
     * @return the chosen format
     * - encoding: unused
     * - decoding: Set by user, if not set the native format will be chosen.
     */
    enum AVPixelFormat (*get_format)(struct AVCodecContext *s, const enum AVPixelFormat * fmt);

    /**
     * maximum number of B-frames between non-B-frames
     * Note: The output will be delayed by max_b_frames+1 relative to the input.
     * - 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;

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int b_frame_strategy;
#endif

    /**
     * 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;

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int mpeg_quant;
#endif

    /**
     * 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;

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
     int prediction_method;
#define FF_PRED_LEFT   0
#define FF_PRED_PLANE  1
#define FF_PRED_MEDIAN 2
#endif

    /**
     * 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;

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int pre_me;
#endif

    /**
     * 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;

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int scenechange_threshold;

    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int noise_reduction;
#endif

    /**
     * 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;

#if FF_API_PRIVATE_OPT
    /**
     * @deprecated use encoder private options instead
     */
    attribute_deprecated
    int me_penalty_compensation;
#endif

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

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int brd_scale;
#endif

    /**
     * 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;

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int chromaoffset;
#endif

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

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int b_sensitivity;
#endif

    /**
     * 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
    int channels;    ///< number of audio channels

    /**
     * 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;

    /**
     * Audio channel layout.
     * - encoding: set by user.
     * - decoding: set by user, may be overwritten by libavcodec.
     */
    uint64_t channel_layout;

    /**
     * Request decoder to use this channel layout if it can (0 for default)
     * - encoding: unused
     * - decoding: Set by user.
     */
    uint64_t request_channel_layout;

    /**
     * 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 and thread_safe_callbacks is set,
     * 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);

    /**
     * If non-zero, the decoded audio and video frames returned from
     * avcodec_decode_video2() and avcodec_decode_audio4() are reference-counted
     * and are valid indefinitely. The caller must free them with
     * av_frame_unref() when they are not needed anymore.
     * Otherwise, the decoded frames must not be freed by the caller and are
     * only valid until the next decode call.
     *
     * This is always automatically enabled if avcodec_receive_frame() is used.
     *
     * - encoding: unused
     * - decoding: set by the caller before avcodec_open2().
     */
    attribute_deprecated
    int refcounted_frames;

    /* - 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,  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,  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;

#if FF_API_CODER_TYPE
#define FF_CODER_TYPE_VLC       0
#define FF_CODER_TYPE_AC        1
#define FF_CODER_TYPE_RAW       2
#define FF_CODER_TYPE_RLE       3
    /**
     * @deprecated use encoder private options instead
     */
    attribute_deprecated
    int coder_type;
#endif /* FF_API_CODER_TYPE */

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int context_model;
#endif

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int frame_skip_threshold;

    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int frame_skip_factor;

    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int frame_skip_exp;

    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int frame_skip_cmp;
#endif /* FF_API_PRIVATE_OPT */

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

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int min_prediction_order;

    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int max_prediction_order;

    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int64_t timecode_frame_start;
#endif

#if FF_API_RTP_CALLBACK
    /**
     * @deprecated unused
     */
    /* The RTP callback: This function is called    */
    /* every time the encoder has a packet to send. */
    /* It depends on the encoder if the data starts */
    /* with a Start Code (it should). H.263 does.   */
    /* mb_nb contains the number of macroblocks     */
    /* encoded in the RTP payload.                  */
    attribute_deprecated
    void (*rtp_callback)(struct AVCodecContext *avctx, void *data, int size, int mb_nb);
#endif

#if FF_API_PRIVATE_OPT
    /** @deprecated use encoder private options instead */
    attribute_deprecated
    int rtp_payload_size;   /* The size of the RTP payload: the coder will  */
                            /* do its best to deliver a chunk with size     */
                            /* below rtp_payload_size, the chunk will start */
                            /* with a start code on some codecs like H.263. */
                            /* This doesn't take account of any particular  */
                            /* headers inside the transmitted RTP payload.  */
#endif

#if FF_API_STAT_BITS
    /* statistics, used for 2-pass encoding */
    attribute_deprecated
    int mv_bits;
    attribute_deprecated
    int header_bits;
    attribute_deprecated
    int i_tex_bits;
    attribute_deprecated
    int p_tex_bits;
    attribute_deprecated
    int i_count;
    attribute_deprecated
    int p_count;
    attribute_deprecated
    int skip_count;
    attribute_deprecated
    int misc_bits;

    /** @deprecated this field is unused */
    attribute_deprecated
    int frame_bits;
#endif

    /**
     * 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
#if FF_API_DEBUG_MV
/**
 * @deprecated this option does nothing
 */
#define FF_DEBUG_MV          32
#endif
#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
#if FF_API_DEBUG_MV
#define FF_DEBUG_VIS_QP      0x00002000
#define FF_DEBUG_VIS_MB_TYPE 0x00004000
#endif
#define FF_DEBUG_BUFFERS     0x00008000
#define FF_DEBUG_THREADS     0x00010000
#define FF_DEBUG_GREEN_MD    0x00800000
#define FF_DEBUG_NOMC        0x01000000

#if FF_API_DEBUG_MV
    /**
     * debug
     * - encoding: Set by user.
     * - decoding: Set by user.
     */
    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

    /**
     * Error recognition; may misdetect some more or less valid parts as errors.
     * - encoding: unused
     * - 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
     * is. e.g. for VA API, this is a struct vaapi_context.
     * - 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
#define FF_IDCT_NONE          24 /* Used by XvMC to extract IDCT coefficients with FF_IDCT_PERM_NONE */
#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;

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

#if FF_API_CODED_FRAME
    /**
     * the picture in the bitstream
     * - encoding: Set by libavcodec.
     * - decoding: unused
     *
     * @deprecated use the quality factor packet side data instead
     */
    attribute_deprecated AVFrame *coded_frame;
#endif

    /**
     * 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;

    /**
     * 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.
     */
    int thread_safe_callbacks;

    /**
     * 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.
     * Also see avcodec_thread_init and e.g. the --enable-pthread configure option.
     * @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_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

    /**
     * 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;

#if FF_API_VBV_DELAY
    /**
     * VBV delay coded in the last frame (in periods of a 27 MHz clock).
     * Used for compliant TS muxing.
     * - encoding: Set by libavcodec.
     * - decoding: unused.
     * @deprecated this value is now exported as a part of
     * AV_PKT_DATA_CPB_PROPERTIES packet side data
     */
    attribute_deprecated
    uint64_t vbv_delay;
#endif

#if FF_API_SIDEDATA_ONLY_PKT
    /**
     * Encoding only and set by default. Allow encoders to output packets
     * that do not contain any encoded data, only side data.
     *
     * Some encoders need to output such packets, e.g. to update some stream
     * parameters at the end of encoding.
     *
     * @deprecated this field disables the default behaviour and
     *             it is kept only for compatibility.
     */
    attribute_deprecated
    int side_data_only_packets;
#endif

    /**
     * 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;

    /**
     * Nominal unaccelerated pixel format, see 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;

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

    /**
     * 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
    /**
     * debug motion vectors
     * - encoding: Set by user.
     * - decoding: Set by user.
     */
    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

    /**
     * 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;

    /**
     * Control the form of AVSubtitle.rects[N]->ass
     * - decoding: set by user
     * - encoding: unused
     */
    int sub_text_format;
#define FF_SUB_TEXT_FMT_ASS              0
#if FF_API_ASS_TIMING
#define FF_SUB_TEXT_FMT_ASS_WITH_TIMINGS 1
#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;

    /**
     * A reference to the AVHWDeviceContext describing the device which will
     * be used by a hardware encoder/decoder.  The reference is set by the
     * caller and afterwards owned (and freed) by libavcodec.
     *
     * 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;
} AVCodecContext;

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