H264解码深度解析——DM8168 OMX从H264文件读取一帧数据(do chunking of h264)

源码来源：TI - DM8168 - EZSDK - OMX - examples - decode_display

基本执行流程如下：

Decode_GetNextFrameSize(H264_ParsingCtx *pc)函数源码（加注释）如下：

/*****************************************************************************\
*     Decode_GetNextFrameSize Function Declaration
\*****************************************************************************/
/**
*
* @brief    Gets the size of thenext frame, It is doing chunking of h264
*           elementary bitstream and providing frames to OMX component.
*
* @param in:
*           pc: Pointer to H264_ParsingCtx structure
*
* @param Out:
*           None
*
* @return   uint32_t - Frame Size
*
*/
 
unsigned int Decode_GetNextFrameSize(H264_ParsingCtx *pc)
{
 FILE *fp = pc->fp; // pc->fp指向的是H264文件
 unsigned char *readBuf = pc->readBuf;
 H264_ChunkingCtx *ctx = &pc->ctx;
 AVChunk_Buf *inBuf = &pc->inBuf;
 AVChunk_Buf *outBuf = &pc->outBuf;
 
 unsigned char termCond = 1;
  if(pc->firstParse == 1) // pc->firstParse的初始化值就是1
   termCond = 0;
 
 while ((!feof (fp)) ||
        ((((pc->firstParse == 0) && (pc->bytes != 0))
          && (pc->bytes <= READSIZE) && (pc->tmp <=pc->bytes))))
  {
   if (pc->firstParse == 1)
    {
     pc->bytes = fread (readBuf, 1, READSIZE, fp);//将H264比特流读取到readBuf
     if (!pc->bytes)
     {
       return 0;
     }
     inBuf->ptr = readBuf;  // inBuf->ptr也指向了H264比特流数据
     pc->tmp = 0;
     pc->firstParse = 0;
    }
   else
    {
     if (pc->bytes <= pc->tmp)
     {
       pc->bytes = fread (readBuf, 1, READSIZE, fp);
       if (!pc->bytes)
       {
         return 0;
       }
       inBuf->ptr = readBuf;
       pc->tmp = 0;
     }
    }
 
   while (pc->bytes > pc->tmp)
    {
     inBuf->bufsize =
       ((pc->bytes - pc->tmp) > 184) ? 184 : (pc->bytes -pc->tmp)