/**
* This structure stores compressed data. It is typically exported by demuxers * and then passed as input to decoders, or received as output from encoders and * then passed to muxers. *AVPacket就是一个存储压缩之后的数据的结构体。1 由demuxer产生传给decoder；或者2 从encoder接收传给muxer * For video, it should typically contain one compressed frame. For audio it may * contain several compressed frames.对于视频对应一帧，对于音频对应多帧 * * AVPacket is one of the few structs in FFmpeg, whose size is a part of public * ABI. Thus it may be allocated on stack and no new fields can be added to it * without libavcodec and libavformat major bump. * * The semantics of data ownership depends on the buf or destruct (deprecated) * fields. If either is set, the packet data is dynamically allocated and is * valid indefinitely until av_free_packet() is called (which in turn calls * av_buffer_unref()/the destruct callback to free the data). If neither is set, * the packet data is typically backed by some static buffer somewhere and is * only valid for a limited time (e.g. until the next read call when demuxing). * * The side data is always allocated with av_malloc() and is freed in * av_free_packet(). */packet的数据是动态分配并且直到av_free_packet()被调用之前还有效。
它的旁路数据总是由av_malloc()分配并且用av_free_pakcet()来释放。
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;//呈现给用户的时间戳 /** * 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;//解压缩的时间戳 uint8_t *data;//数据，特别注意在解码的时候每次用av_read_frame()读完一帧到AVPacket之后要用av_free_packet()函数来释放掉数据一次，才去读下一帧 int size;//数据的大小 int stream_index;//标志流的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;