VideoToolBox兼容不标准的多slice视频 --转自：网易云信
在iOS平台的硬解的实践中，我们可能会遇到如下图的这种情况（上面一部分有画面，下面部分是绿屏）：
这种现象实际上就是多slice视频的组织格式不符合VideoToolBox的要求引起的。一般出现在某些华为手机，小米手机，编码大分辨率视频流的时候，进行分片编码。
以上图的视频为例，该视频流的每一帧是由3个slice构成的，对于VideoToolBox可以正常解码的组织格式应该如下图所示：
而该视频的帧组织方式则如下图所示：
可以看出，该视频混用了AVCC与Annex-B格式的分隔符，导致iOS VideoToolBox只能解码第一个slice单元，从而出现下半部分绿屏的情况。
- 对于这类问题视频的处理： 如果是源视频流可控，可以调整源视频流的打包方式，按第一种图示的方式打包。
- 对于不可控的场景，播放器也可以做下兼容：因为一个NALU中的内容一定是不包含startcode的，所以如果在一个NALU中找到了startcode，就可以将其处理成第一种图示中的格式。
修改方式寻找一帧中的起始码，通过计算字节差，计算每个片的size，将片段中的00000001替换成新计算的size（每片对应自己的size）
以下边简单地两片为例：
unsigned char* bufferOneFream, unsigned int buffFreanLen, h264的数据和长度
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int naluType = 0; unsigned int oneFreamIndex = 0; unsigned int spsIndex = 0; unsigned int ppsIndex = 0; unsigned char* spsPtr = NULL; unsigned char* ppsPtr = NULL; unsigned char* framePtr = NULL; unsigned int contentLen = 0; //有效码流长度 unsigned char imgLenArr[4]={0}; //起使码转换成长度子节 static unsigned int spsLen ; //sps字段长度 static unsigned int ppsLen ; //pps字段长度 static unsigned char* spsBuff; //sps字段缓存 static unsigned char* ppsBuff; unsigned char* contentFream; bool multislice; CVPixelBufferRef pixelbuffer = NULL; //该帧数据，硬解的结果 while(oneFreamIndex < (buffFrameLen)) //start code { multislice = false;//默认非多slice if(bufferOneFream[oneFreamIndex] == 0x00 && bufferOneFream[oneFreamIndex + 1] == 0x00 && bufferOneFream[oneFreamIndex + 2] == 0x00 && bufferOneFream[oneFreamIndex + 3] == 0x01) { naluType = (bufferOneFream[oneFreamIndex + 4]) & 0x0F; switch(naluType) { case 0x06:// SEI break; case 0x09://aud //std::cout<<"aud"<<std::endl; break; case 0x07: //sps //std::cout<<"sps"<<std::endl; spsPtr = &bufferOneFream[oneFreamIndex + 4]; spsIndex = oneFreamIndex + 4; break; case 0x08: //std::cout<<"pps"<<std::endl; //pps ppsPtr = &bufferOneFream[oneFreamIndex + 4]; ppsIndex = oneFreamIndex + 4; spsBuff=(unsigned char*)malloc(ppsIndex-spsIndex-4); memcpy(spsBuff,spsPtr,(ppsIndex-spsIndex-4)); //memcpy sps spsLen = ppsIndex-spsIndex-4; break; case 0x05://i frame //std::cout<<"i fream"<<std::endl; { ppsBuff=(unsigned char*)malloc(oneFreamIndex - ppsIndex); memcpy(ppsBuff,ppsPtr,(oneFreamIndex - ppsIndex)); //memcpy pps ppsLen = oneFreamIndex - ppsIndex; //memcpy PPS ////I帧内容 framePtr = &bufferOneFream[oneFreamIndex + 4]; //内容流的位置 contentLen = buffFreanLen - (oneFreamIndex + 4); //内容流的长度，不包含4字节start code int nalu_size1 =0; int nale_size2 =0; int nextStartcode = 0; for(int index2 = 0; index2< contentLen;index2++) { if(bufferOneFream[oneFreamIndex + 4+ index2]==0x00 && bufferOneFream[oneFreamIndex + 5+ index2] == 0x00 && bufferOneFream[oneFreamIndex + 6+ index2] == 0x00 && bufferOneFream[oneFreamIndex + 7+ index2] == 0x01)////找第二个nale 的start code { nextStartcode = index2; multislice = true; break; } } if(multislice == true) { NSLog(@"i yes"); nalu_size1 = nextStartcode; nale_size2 = contentLen - nextStartcode - 4;///slice2的内容要减去前边的四个字节 bufferOneFream[oneFreamIndex + 4+ nalu_size1]=(nale_size2 & 0xff000000)>>24; bufferOneFream[oneFreamIndex + 5+ nalu_size1] = (nale_size2 & 0x00ff0000)>>16; bufferOneFream[oneFreamIndex + 6+ nalu_size1] = (nale_size2 & 0x0000ff00)>>8; bufferOneFream[oneFreamIndex + 7+ nalu_size1] = (nale_size2 & 0x000000ff); //////// imgLenArr[0] = (nalu_size1 & 0xff000000)>>24; //大端码流长度转换 imgLenArr[1] = (nalu_size1 & 0x00ff0000)>>16; imgLenArr[2] = (nalu_size1 & 0x0000ff00)>>8; imgLenArr[3] = nalu_size1 & 0x000000ff; // imgLenArr[0] = (contentLen & 0xff000000)>>24; //大端码流长度转换 // imgLenArr[1] = (contentLen & 0x00ff0000)>>16; // imgLenArr[2] = (contentLen & 0x0000ff00)>>8; // imgLenArr[3] = contentLen & 0x000000ff; // contentFream = (unsigned char*)malloc(contentLen + 4); memcpy(contentFream,imgLenArr, 4); memcpy(contentFream+4 ,framePtr, contentLen); //表示长度的四个字节和码流内容 pixelbuffer = HardDecode(contentFream,contentLen+4, spsBuff, spsLen, ppsBuff, ppsLen,1);//解码后数据 /////复位 multislice = false; //保存yuv数据/////////////////////////////////////////////////////////////////// //SaveYUV(pixelbuffer, fout); free(contentFream); return pixelbuffer; }else{////signal slice NSLog(@"i no"); imgLenArr[0] = (contentLen & 0xff000000)>>24; //大端码流长度转换 imgLenArr[1] = (contentLen & 0x00ff0000)>>16; imgLenArr[2] = (contentLen & 0x0000ff00)>>8; imgLenArr[3] = contentLen & 0x000000ff; contentFream = (unsigned char*)malloc(contentLen + 4); memcpy(contentFream,imgLenArr, 4); memcpy(contentFream+4 ,framePtr, contentLen); //表示长度的四个字节和码流内容 pixelbuffer = HardDecode(contentFream,contentLen+4, spsBuff, spsLen, ppsBuff, ppsLen,1);//解码后数据 //保存yuv数据/////////////////////////////////////////////////////////////////// //SaveYUV(pixelbuffer, fout); free(contentFream); return pixelbuffer; } } case 0x01://p fream { //std::cout<<"p fream"<<std::endl; framePtr = &bufferOneFream[oneFreamIndex + 4]; contentLen = buffFreanLen - (oneFreamIndex + 4); int nalu_size1 =0; int nale_size2 =0; int nextStartcode = 0; for(int index2 = 0; index2< contentLen;index2++) { if(bufferOneFream[oneFreamIndex + 4+ index2]==0x00 && bufferOneFream[oneFreamIndex + 5+ index2] == 0x00 && bufferOneFream[oneFreamIndex + 6+ index2] == 0x00 && bufferOneFream[oneFreamIndex + 7+ index2] == 0x01) { nextStartcode = index2; multislice = true; break; } } if(multislice == true) { NSLog(@"p yes"); nalu_size1 = nextStartcode; nale_size2 = contentLen - nextStartcode - 4;///slice2的内容要减去前边的四个字节 bufferOneFream[oneFreamIndex + 4+ nalu_size1]=(nale_size2 & 0xff000000)>>24; bufferOneFream[oneFreamIndex + 5+ nalu_size1] = (nale_size2 & 0x00ff0000)>>16; bufferOneFream[oneFreamIndex + 6+ nalu_size1] = (nale_size2 & 0x0000ff00)>>8; bufferOneFream[oneFreamIndex + 7+ nalu_size1] = (nale_size2 & 0x000000ff); //////// imgLenArr[0] = (nalu_size1 & 0xff000000)>>24; //大端码流长度转换 imgLenArr[1] = (nalu_size1 & 0x00ff0000)>>16; imgLenArr[2] = (nalu_size1 & 0x0000ff00)>>8; imgLenArr[3] = nalu_size1 & 0x000000ff; contentFream = (unsigned char*)malloc(contentLen + 4); //转换成标准格式的一帧数据 memcpy(contentFream,imgLenArr, 4); memcpy(contentFream+4 ,framePtr, contentLen); NSLog(@"buffFreanLen %d,contentLen %d,nalu_size1 %d,nale_size2 %d",buffFreanLen,contentLen,nalu_size1,nale_size2); pixelbuffer = HardDecode(contentFream, contentLen+4, spsBuff, spsLen, ppsBuff, ppsLen,0); //保存yuv数据/////////////////////////////////////////////////////////////////// //SaveYUV(pixelbuffer, fout); multislice = false ; free(contentFream); return pixelbuffer ; }else{///p slgnal slice NSLog(@"p no"); imgLenArr[0] = (contentLen & 0xff000000)>>24; //大端码流长度转换 imgLenArr[1] = (contentLen & 0x00ff0000)>>16; imgLenArr[2] = (contentLen & 0x0000ff00)>>8; imgLenArr[3] = contentLen & 0x000000ff; contentFream = (unsigned char*)malloc(contentLen + 4); //转换成标准格式的一帧数据 memcpy(contentFream,imgLenArr, 4); memcpy(contentFream+4 ,framePtr, contentLen); pixelbuffer = HardDecode(contentFream, contentLen+4, spsBuff, spsLen, ppsBuff, ppsLen,0); //保存yuv数据/////////////////////////////////////////////////////////////////// //SaveYUV(pixelbuffer, fout); free(contentFream); return pixelbuffer ; } } default://other, break; }