如何用SPS和PPS数据填充AVCodecContext的“额外数据"字段?

问题描述

这是问题所在:用ffmpeg解码H264流时，我可以获得SPS和PPS的原始数据，但是我不知道如何将它们填充到AVCodecContext的extradata字段中.没有extradata，我将无法正确解码帧.每次调用avcodec_decodec_video2时，返回值为正，但got_picture标志始终为zero.

Here is the problem: When decoding H264 stream with ffmpeg, I can obtain raw data of SPS and PPS but I have no idea how to fill them into the extradata field of AVCodecContext. Without extradata, I can't decode frames properly. Every time I call avcodec_decodec_video2, the return value is positive but the got_picture flag is always zero.

我正在处理的流看起来像这样:

The stream I am dealing with looks like this:

[0x67]...[0x68]...[0x61]...[0x61]...  .......  [0x61]...[0x67]...[0x68]...  ......

推荐答案

您提到的数据是一个字节流，其中包含用于SPS和PPS的NAL单元. extradata反过来需要一个指向AVC解码器配置记录的指针，这是您具有额外格式的数据.

The data you mentioned is a byte stream holding NAL units for SPS and PPS. extradata in turn expects a pointer to AVC decoder configuration record, which is the data you have with extra formatting.

有关详细信息，请参见MPEG-4第15部分高级视频编码(AVC)文件格式"部分.

See MPEG-4 Part 15 "Advanced Video Coding (AVC) file format" section 5.2.4.1 for details.

5.2.4.1.1 Syntax

aligned(8) class AVCDecoderConfigurationRecord {
   unsigned int(8) configurationVersion = 1;
   unsigned int(8) AVCProfileIndication;
   unsigned int(8) profile_compatibility;
   unsigned int(8) AVCLevelIndication;
   bit(6) reserved = ‘111111’b;
   unsigned int(2) lengthSizeMinusOne;
   bit(3) reserved = ‘111’b;
   unsigned int(5) numOfSequenceParameterSets;
   for (i=0; i< numOfSequenceParameterSets;  i++) {
      unsigned int(16) sequenceParameterSetLength ;
  bit(8*sequenceParameterSetLength) sequenceParameterSetNALUnit;
 }
   unsigned int(8) numOfPictureParameterSets;
   for (i=0; i< numOfPictureParameterSets;  i++) {
  unsigned int(16) pictureParameterSetLength;
  bit(8*pictureParameterSetLength) pictureParameterSetNALUnit;
 }
}

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