在上文我们学习了AVStream结构体的相关内容。本文，我们将讲述一下AVPacket。

AVPacket是存储压缩编码数据相关信息的结构体。下面我们来分析一下该结构体里重要变量的含义和作用。

一、源码整理

首先我们先看一下结构体AVPacket的定义的结构体源码(位于libavcodec/avcodec.h)：

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;

二、AVPacket 重点字段

uint8_t *data：压缩编码的数据。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所属的视频/音频流。

针对data做一下说明：对于H.264格式来说，在使用FFMPEG进行视音频处理的时候，我们常常可以将得到的AVPacket的data数据直接写成文件，从而得到视音频的码流文件。