ffmpeg结构体熟悉——AVIOContext

最新推荐文章于 2024-08-01 07:19:14 发布

easyhao007

最新推荐文章于 2024-08-01 07:19:14 发布

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本文详细介绍了FFmpeg中AVIOContext结构体的各个字段含义及作用。AVIOContext用于抽象文件I/O操作，支持多种读写操作及寻址方式，适用于不同网络流媒体协议。

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typedef struct AVIOContext {
    /**
     * A class for private options.
     *
     * If this AVIOContext is created by avio_open2(), av_class is set and
     * passes the options down to protocols.
     *
     * If this AVIOContext is manually allocated, then av_class may be set by
     * the caller.
     *
     * warning -- this field can be NULL, be sure to not pass this AVIOContext
     * to any av_opt_* functions in that case.
     */
    const AVClass 			*av_class;
    unsigned char 		*buffer;  				/**< Start of the buffer. */
    int 								buffer_size; 		/**< Maximum buffer size */
    unsigned char 		*buf_ptr; 			/**< Current position in the buffer */
    unsigned char 		*buf_end; /**< End of the data, may be less than
                                 buffer+buffer_size if the read function returned
                                 less data than requested, e.g. for streams where
                                 no more data has been received yet. */
    void *opaque;           /**< A private pointer, passed to the read/write/seek/... functions. */

    int (*read_packet)(void *opaque, uint8_t *buf, int buf_size);
    int (*write_packet)(void *opaque, uint8_t *buf, int buf_size);
    int64_t (*seek)(void *opaque, int64_t offset, int whence);
    int64_t pos;            		/**< position in the file of the current buffer */
    int must_flush;         	/**< true if the next seek should flush */
    int eof_reached;        /**< true if eof reached */
    int write_flag;         	/**< true if open for writing */
    int max_packet_size;
    unsigned long checksum;
    unsigned char *checksum_ptr;
    unsigned long (*update_checksum)(unsigned long checksum, const uint8_t *buf, unsigned int size);
    int error;              /**< contains the error code or 0 if no error happened */
    /**
     * Pause or resume playback for network streaming protocols - e.g. MMS.  暂停或从新开始
     */
    int (*read_pause)(void *opaque, int pause);
    /**
     * Seek to a given timestamp in stream with the specified stream_index.	seek到一个给定的时间戳
     * Needed for some network streaming protocols which don't support seeking
     * to byte position.
     */
    int64_t (*read_seek)(void *opaque, int stream_index,
                         int64_t timestamp, int flags);
    /**
     * A combination of AVIO_SEEKABLE_ flags or 0 when the stream is not seekable.
     */
    int seekable;

    /**
     * max filesize, used to limit allocations
     * This field is internal to libavformat and access from outside is not allowed.
     */
    int64_t maxsize;

    /**
     * avio_read and avio_write should if possible be satisfied directly
     * instead of going through a buffer, and avio_seek will always
     * call the underlying seek function directly.
     */
    int direct;

    /**
     * Bytes read statistic
     * This field is internal to libavformat and access from outside is not allowed.
     */
    int64_t bytes_read;

    /**
     * seek statistic
     * This field is internal to libavformat and access from outside is not allowed.
     */
    int seek_count;

    /**
     * writeout statistic
     * This field is internal to libavformat and access from outside is not allowed.
     */
    int writeout_count;
} AVIOContext;