typedef struct AVPacket {
/**
* A reference to the reference-counted buffer where the packet data is
* stored.
* May be NULL, then the packet data is not reference-counted.
*/
AVBufferRef *buf;
/**
* 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.
*/
AVPacketSideData *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.
*/
int64_t duration;

int64_t pos; ///< byte position in stream, -1 if unknown

#if FF_API_CONVERGENCE_DURATION
/**
* @deprecated Same as the duration field, but as int64_t. This was required
* for Matroska subtitles, whose duration values could overflow when the
* duration field was still an int.
*/
attribute_deprecated
int64_t convergence_duration;
#endif
} AVPacket;

用来存放引用计数的数据，如果没有使用引用计数，值就是NULL，当你多个packet对象引用同一帧数据的时候用到。

本帧数据显示的时间，比较关键的数据，在做seek和播放进度的时候都要用到它，pts只是一个数量，对应于AVStream->time_base，要根据time_base才能转换为具体的时间,音频和视频一般有不同的time_base，所以在做音视频同步一定要做转换，不能直接拿pts做。

转换方式，比如转为毫秒

AVFormatContext *ic = NULL;

static double r2d(AVRational r)

{

return r.num == 0 || r.den == 0 ? 0. : (double)r.num / (double)r.den;

}

//。。。

int pts = (pkt->pts *r2d(ic->streams[pkt->stream_index]->time_base)) * 1000;

基本属性等同于pts，区别就是dts对应的是解码时间不是显示时间，解码后会放入缓冲，比如h264，如果有b帧，则要先解码后面的b帧，再解码之前的帧。

帧的数据和数据大小

标志，其中为1表示该数据是一个关键帧

AV_PKT_FLAG_KEY 0x0001 关键帧

AVPacketSideData *side_data;

容器提供的一些附加数据