ffmpeg数据结构-AVFormatContext

/** * 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. */typedef struct AVFormatContext {    /**     * A class for logging and AVOptions. Set by avformat_alloc_context().     * Exports (de)muxer private options if they exist.     */    const AVClass *av_class;    /**     * Can only be iformat or oformat, not both at the same time.     *     * decoding: set by avformat_open_input().     * encoding: set by the user.    in和out只能选其一     */    struct AVInputFormat *iformat;    struct AVOutputFormat *oformat;    /**     * Format private data. This is an AVOptions-enabled struct     * if and only if iformat/oformat.priv_class is not NULL.     */    void *priv_data;    /**     * I/O context.     *输入输出上下问     * decoding: either set by the user before avformat_open_input() (then     * 解码：既可以被设置在avformat_open_input()之前（当然用户必须关闭他随后）     * the user must close it manually) or set by avformat_open_input().     * 或则可以被avformat_open_input()设置     * encoding: set by the user.     *编码：设置被用户     * 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  流的信息  设置的值  见AVFMTCTX_NOHEADER 等*/    int ctx_flags; /**< Format-specific flags, see AVFMTCTX_xx */    /**     * A list of all streams in the file. New streams are created with     * avformat_new_stream().     *streams:一个列表  表示一个文件中所有的流     *     * decoding: 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().     * encoding: streams are created by the user before avformat_write_header().     */    unsigned int nb_streams;    AVStream **streams;    char filename[1024]; /**< input or output filename */    /**     * Decoding: 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.     */    int64_t start_time;    /**     * Decoding: 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.     */    int64_t duration;    /**     * Decoding: 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.     */    int bit_rate;    unsigned int packet_size;    int max_delay;    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.#define AVFMT_FLAG_MP4A_LATM    0x8000 ///< Enable RTP MP4A-LATM payload#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)#define AVFMT_FLAG_KEEP_SIDE_DATA 0x40000 ///< Don't merge side data but keep it separate.    /**     * decoding: size of data to probe; encoding: unused.     */    unsigned int probesize;    /**     * decoding: maximum time (in AV_TIME_BASE units) during which the input should     * be analyzed in avformat_find_stream_info().     */    int 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.     * 要使用索引的每个流中的字节中的内存的最大数量。如果索引超过此大小，条目将被丢弃，     * 因为需要保持较小的大小。这可以导致较慢或不太准确寻找 （取决于分离器）。     * 全部内存索引是强制性的 Demuxers 会忽视这一点。     * 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;    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.     * - encoding: Set by user.     * - decoding: Unused.     */    int64_t start_time_realtime;    /**     * decoding: number of frames used to probe fps     */    int fps_probe_size;    /**     * Error recognition; higher values will detect more errors but may     * misdetect some more or less valid parts as errors.     * - encoding: unused     * - decoding: Set by user.     */    int error_recognition;    /**     * Custom interrupt callbacks for the I/O layer.     *     * decoding: set by the user before avformat_open_input().     * encoding: 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    /**     * Transport stream id.     * This will be moved into demuxer private options. Thus no API/ABI compatibility     */    int ts_id;    /**     * Audio preload in microseconds.微秒     * Note, not all formats support this and unpredictable things may happen if it is used when not supported.     * - encoding: Set by user via AVOptions (NO direct access)     * - 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 via AVOptions (NO direct access)     * - 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 via AVOptions (NO direct access)     * - 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 via AVOptions (NO direct access)     */    int use_wallclock_as_timestamps;    /**     * Avoid negative timestamps during muxing.     *  0 -> allow negative timestamps     *  1 -> avoid negative timestamps     * -1 -> choose automatically (default)     * Note, this only works when interleave_packet_per_dts is in use.     * - encoding: Set by user via AVOptions (NO direct access)     * - decoding: unused     */    int avoid_negative_ts;    /**     * avio flags, used to force AVIO_FLAG_DIRECT.     * - encoding: unused     * - decoding: Set by user via AVOptions (NO direct access)     */    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 via AVOptions (NO direct access)     */    enum AVDurationEstimationMethod duration_estimation_method;    /**     * Skip initial bytes when opening stream     * - encoding: unused     * - decoding: Set by user via AVOptions (NO direct access)     */    unsigned int skip_initial_bytes;    /**     * Correct single timestamp overflows     * - encoding: unused     * - decoding: Set by user via AVOPtions (NO direct access)     */    unsigned int correct_ts_overflow;    /**     * Force seeking to any (also non key) frames.     * - encoding: unused     * - decoding: Set by user via AVOPtions (NO direct access)     */    int seek2any;    /**     * Flush the I/O context after each packet.     * - encoding: Set by user via AVOptions (NO direct access)     * - 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 via av_format_get_probe_score() (NO direct access)     */    int probe_score;    /*****************************************************************     * All fields below this line are not part of the public API. They     * may not be used outside of libavformat and can be changed and     * removed at will.     * New public fields should be added right above.     *****************************************************************     */    /**     * This buffer is only needed when packets were already buffered but     * not decoded, for example to get the codec parameters in MPEG     * streams.     */    struct AVPacketList *packet_buffer;    struct AVPacketList *packet_buffer_end;    /* av_seek_frame() support */    int64_t data_offset; /**< offset of the first packet */    /**     * Raw packets from the demuxer, prior to parsing and decoding.     * This buffer is used for buffering packets until the codec can     * be identified, as parsing cannot be done without knowing the     * codec.     */    struct AVPacketList *raw_packet_buffer;    struct AVPacketList *raw_packet_buffer_end;    /**     * Packets split by the parser get queued here.     */    struct AVPacketList *parse_queue;    struct AVPacketList *parse_queue_end;    /**     * Remaining size available for raw_packet_buffer, in bytes.     */#define RAW_PACKET_BUFFER_SIZE 2500000    int raw_packet_buffer_remaining_size;    /**     * 偏移量来重新映射为非负的时间戳。     * Offset to remap timestamps to be non-negative.     * Expressed in timebase units.     * @see AVStream.mux_ts_offset     */    int64_t offset;    /**     * Timebase for the timestamp offset.     */    AVRational offset_timebase;    /**     * 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 via av_format_set_video_codec (NO direct access).     */    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 via av_format_set_audio_codec (NO direct access).     */    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 via av_format_set_subtitle_codec (NO direct access).     */    AVCodec *subtitle_codec;} AVFormatContext;