/*该结构存储压缩数据。它通常由分路器导出
*然后作为输入传递给解码器，或作为编码器和输出接收
*然后传递给muxers。
*
*对于视频，它通常应包含一个压缩帧。对于音频它可能
*包含几个压缩帧。
*
* AVPacket是FFmpeg中为数不多的结构之一，其大小是公众的一部分
* ABI。因此，它可以在堆栈上分配，并且不能向其添加新字段
*没有libavcodec和libavformat主要的颠簸。
*
*数据所有权的语义取决于buf或destruct（不建议使用）
*字段。如果设置了任何一个，则分组数据是动态分配的
*无限期有效，直到调用av_free_packet（）（然后调用
* av_buffer_unref（）/解析回调以释放数据）。如果两者都没有，
*数据包数据通常由某个静态缓冲区支持
*仅在有限时间内有效（例如，在解复用时进行下一次读取呼叫）。
*
*副数据总是用av_malloc（）分配并被释放
* av_free_packet（）。
*/
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.
*/
int duration;
#if FF_API_DESTRUCT_PACKET
attribute_deprecated
void (*destruct)(struct AVPacket *);
attribute_deprecated
void *priv;
#endif
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;