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95 lines
3.1 KiB
95 lines
3.1 KiB
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。
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# 一、源码整理
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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)：
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```
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typedef struct AVPacket {
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/**
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* Presentation timestamp in AVStream->time_base units; the time at which
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* the decompressed packet will be presented to the user.
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* Can be AV_NOPTS_VALUE if it is not stored in the file.
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* pts MUST be larger or equal to dts as presentation cannot happen before
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* decompression, unless one wants to view hex dumps. Some formats misuse
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* the terms dts and pts/cts to mean something different. Such timestamps
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* must be converted to true pts/dts before they are stored in AVPacket.
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*/
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int64_t pts;
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/**
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* Decompression timestamp in AVStream->time_base units; the time at which
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* the packet is decompressed.
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* Can be AV_NOPTS_VALUE if it is not stored in the file.
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*/
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int64_t dts;
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uint8_t *data;
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int size;
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int stream_index;
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/**
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* A combination of AV_PKT_FLAG values
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*/
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int flags;
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/**
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* Additional packet data that can be provided by the container.
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* Packet can contain several types of side information.
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*/
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struct {
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uint8_t *data;
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int size;
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enum AVPacketSideDataType type;
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} *side_data;
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int side_data_elems;
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/**
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* Duration of this packet in AVStream->time_base units, 0 if unknown.
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* Equals next_pts - this_pts in presentation order.
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*/
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int duration;
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void (*destruct)(struct AVPacket *);
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void *priv;
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int64_t pos; ///< byte position in stream, -1 if unknown
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/**
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* Time difference in AVStream->time_base units from the pts of this
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* packet to the point at which the output from the decoder has converged
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* independent from the availability of previous frames. That is, the
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* frames are virtually identical no matter if decoding started from
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* the very first frame or from this keyframe.
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* Is AV_NOPTS_VALUE if unknown.
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* This field is not the display duration of the current packet.
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* This field has no meaning if the packet does not have AV_PKT_FLAG_KEY
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* set.
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*
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* The purpose of this field is to allow seeking in streams that have no
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* keyframes in the conventional sense. It corresponds to the
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* recovery point SEI in H.264 and match_time_delta in NUT. It is also
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* essential for some types of subtitle streams to ensure that all
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* subtitles are correctly displayed after seeking.
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*/
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int64_t convergence_duration;
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} AVPacket;
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```
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# 二、AVPacket 重点字段
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```
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uint8_t *data：压缩编码的数据。
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int size：data的大小
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int64_t pts：显示时间戳
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int64_t dts：解码时间戳
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int stream_index：标识该AVPacket所属的视频/音频流。
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```
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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。
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