FFMPEG结构体分析：AVPacket(解码前的数据)

 本文转自： http://blog.csdn.net/leixiaohua1020/article/details/14215755

AVPacket 存放的是解码前的数据

/* 雷霄骅
 * 中国传媒大学/数字电视技术
 * leixiaohua1020@126.com
 *
 */
typedef struct AVPacket {
    /**
     * Presentation timestamp in AVStream->time_base units; the time at which
     * the decompressed packet will be presented to the user.
     * Can be AV_NOPTS_VALUE if it is not stored in the file.
     * pts MUST be larger or equal to dts as presentation cannot happen before
     * decompression, unless one wants to view hex dumps. Some formats misuse
     * the terms dts and pts/cts to mean something different. Such timestamps
     * must be converted to true pts/dts before they are stored in AVPacket.
     */
    int64_t pts;
    /**
     * Decompression timestamp in AVStream->time_base units; the time at which
     * the packet is decompressed.
     * Can be AV_NOPTS_VALUE if it is not stored in the file.
     */
    int64_t dts;
    uint8_t *data;
    int   size;
    int   stream_index;
    /**
     * A combination of AV_PKT_FLAG values
     */
    int   flags;
    /**
     * Additional packet data that can be provided by the container.
     * Packet can contain several types of side information.
     */
    struct {
        uint8_t *data;
        int      size;
        enum AVPacketSideDataType type;
    } *side_data;
    int side_data_elems;

    /**
     * Duration of this packet in AVStream->time_base units, 0 if unknown.
     * Equals next_pts - this_pts in presentation order.
     */
    int   duration;
    void  (*destruct)(struct AVPacket *);
    void  *priv;
    int64_t pos;                            ///< byte position in stream, -1 if unknown

    /**
     * Time difference in AVStream->time_base units from the pts of this
     * packet to the point at which the output from the decoder has converged
     * independent from the availability of previous frames. That is, the
     * frames are virtually identical no matter if decoding started from
     * the very first frame or from this keyframe.
     * Is AV_NOPTS_VALUE if unknown.
     * This field is not the display duration of the current packet.
     * This field has no meaning if the packet does not have AV_PKT_FLAG_KEY
     * set.
     *
     * The purpose of this field is to allow seeking in streams that have no
     * keyframes in the conventional sense. It corresponds to the
     * recovery point SEI in H.264 and match_time_delta in NUT. It is also
     * essential for some types of subtitle streams to ensure that all
     * subtitles are correctly displayed after seeking.
     */
    int64_t convergence_duration;
} AVPacket;

uint8_t *data: 压缩编码的数据

对于H264来主，1个AVPacket的data通常对应一个NAL

因此在使用FFMPEG进行音视频处理的时候，常常可以将得到的AVPacket的data数据直接写入到文件中，从而形成音视频文件。

int  size: data的大小

int64_t pts: 显示时间戳

int64_t dts: 解码时间戳

int stream_index: 标识该AVPacket是哪路音/视频流

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