h264 获取每个nal

一直苦于无法找到比较合适和效率的从内存读取h264的nal的函数，终于不经意间找到了，记录一下：

#define H264_START_CODE 0x000001uint32_t h264_find_next_start_code (uint8_t *pBuf,                    uint32_t bufLen){  uint32_t val;  uint32_t offset;  offset = 0;  if (pBuf[0] == 0 && pBuf[1] == 0 && pBuf[2] == 0 && pBuf[3] == 1) {    pBuf += 4;    offset = 4;  } else if (pBuf[0] == 0 && pBuf[1] == 0 && pBuf[2] == 1) {    pBuf += 3;    offset = 3;  }  val = 0xffffffff;  while (offset < bufLen - 3) {    val <<= 8;    val |= *pBuf++;    offset++;    if (val == H264_START_CODE) {      return offset - 4;    }    if ((val & 0x00ffffff) == H264_START_CODE) {      return offset - 3;    }  }  return 0;}