typedef struct AVInputFormat {
    /**
     * 格式名列表.也可以分配一個新名字.
     */
    const char *name;

    /**
     * 對格式的一個描述性名字,增加可讀性.
     */
    const char *long_name;

    /**
     * 可用的flag有: AVFMT_NOFILE, AVFMT_NEEDNUMBER, AVFMT_SHOW_IDS,
     * AVFMT_GENERIC_INDEX, AVFMT_TS_DISCONT, AVFMT_NOBINSEARCH,
     * AVFMT_NOGENSEARCH, AVFMT_NO_BYTE_SEEK, AVFMT_SEEK_TO_PTS.
     */
    int flags;

    /**
     * 如果定義了extention那麼就不會再檢測了，通常不定義，因為定義的不靠譜
     */
    const char *extensions;

    const struct AVCodecTag * const *codec_tag;

    const AVClass *priv_class; ///< AVClass for the private context

    /**
     * 一個模擬型別列表.用來在probe的時候check匹配的型別
     * @see av_probe_input_format2
     */
    const char *mime_type;

    /*****************************************************************
     * No fields below this line are 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.
     *****************************************************************
     */
    struct AVInputFormat *next;

    /**
     * Raw demuxers store their codec ID here.
     */
    int raw_codec_id;

    /**
     * Size of private data so that it can be allocated in the wrapper.
     */
    int priv_data_size;

    /**
     * tell一個檔案是否可以按照這個格式來解析.
     * 就是保證提供的buffer夠大.
     */
    int (*read_probe)(AVProbeData *);

    /**
     * read格式頭資訊，initialize the AVFormatContext
     * structure. Return 0 if OK. 'avformat_new_stream' should be
     * called to create new streams.
     */
    int (*read_header)(struct AVFormatContext *);

    /**
     * 讀一個packet放入pkt. pts and flags are also
     * set. 'avformat_new_stream' can be called only if the flag
     * AVFMTCTX_NOHEADER is used and only in the calling thread (not in a
     * background thread).
     * @return 0 on success, < 0 on error.
     *         When returning an error, pkt must not have been allocated
     *         or must be freed before returning
     */
    int (*read_packet)(struct AVFormatContext *, AVPacket *pkt);

    /**
     * Close the stream. The AVFormatContext and AVStreams are not
     * freed by this function
     */
    int (*read_close)(struct AVFormatContext *);

    /**
     * seek到一個給定的時間戳相對於stream_index的frames
     * @param stream_index Must not be -1.
     * @param flags Selects which direction should be preferred if no exact
     *              match is available.
     * @return >= 0 on success (but not necessarily the new offset)
     */
    int (*read_seek)(struct AVFormatContext *,
                     int stream_index, int64_t timestamp, int flags);

    /**
     * 得到下一個時間戳in stream[stream_index].time_base units.
     * @return the timestamp or AV_NOPTS_VALUE if an error occurred
     */
    int64_t (*read_timestamp)(struct AVFormatContext *s, int stream_index,
                              int64_t *pos, int64_t pos_limit);

    /**
     * Start/resume playing - only meaningful if using a network-based format
     * (RTSP).
     */
    int (*read_play)(struct AVFormatContext *);

    /**
     * Pause playing - only meaningful if using a network-based format
     * (RTSP).
     */
    int (*read_pause)(struct AVFormatContext *);

    /**
     * Seek to timestamp ts.
     * Seeking will be done so that the point from which all active streams
     * can be presented successfully will be closest to ts and within min/max_ts.
     * Active streams are all streams that have AVStream.discard < AVDISCARD_ALL.
     */
    int (*read_seek2)(struct AVFormatContext *s, int stream_index, int64_t min_ts, int64_t ts, int64_t max_ts, int flags);

    /**
     * Returns device list with it properties.
     * @see avdevice_list_devices() for more details.
     */
    int (*get_device_list)(struct AVFormatContext *s, struct AVDeviceInfoList *device_list);

    /**
     * Initialize device capabilities submodule（子模組）.
     * @see avdevice_capabilities_create() for more details.
     */
    int (*create_device_capabilities)(struct AVFormatContext *s, struct AVDeviceCapabilitiesQuery *caps);

    /**
     * Free device capabilities submodule.
     * @see avdevice_capabilities_free() for more details.
     */
    int (*free_device_capabilities)(struct AVFormatContext *s, struct AVDeviceCapabilitiesQuery *caps);
} AVInputFormat;