一个MPG文件如何知道它是MPEG1还是MPEG2格式？

[hardman]

RT

[cococut]

陆老师实务精选的那本书上有个vodDemo的例子，有一个函数：
void CMediaInfo::CheckMpegFile(const char * inFile)
{
CoInitialize(NULL);

mFileType = FT_MPEG1; // Default
IGraphBuilder * pBuilder = NULL;
CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER,
IID_IGraphBuilder, (void **) &pBuilder);
if (pBuilder)
{
// Create a file source filter
IBaseFilter * pSource = NULL;
WCHAR wcFilePath[MAX_PATH];
MultiByteToWideChar(CP_ACP, 0, inFile, -1, wcFilePath, MAX_PATH);
pBuilder->AddSourceFilter(wcFilePath, L"Source", &pSource);
pSource->Release();

// Create microsoft MPEG-1 Stream Splitter
IBaseFilter * pSplitter = NULL;
CoCreateInstance(CLSID_MPEG1Splitter , NULL, CLSCTX_INPROC_SERVER,
IID_IBaseFilter, (void **)&pSplitter);
pBuilder->AddFilter(pSplitter, L"MPEG-1 Splitter");
pSplitter->Release();

// Try to connect them...
IPin * pOut = GetPinByDirection(pSource, PINDIR_OUTPUT);
IPin * pIn = GetPinByDirection(pSplitter, PINDIR_INPUT);
HRESULT hr = pBuilder->ConnectDirect(pOut, pIn, NULL);
if (FAILED(hr))
{
mFileType = FT_MPEG2;
// Attention here! 1M data at the end of the file!
mCheckOffset2 = mFileSize - 1048576;
}

pBuilder->RemoveFilter(pSplitter);
pBuilder->RemoveFilter(pSource);
pBuilder->Release();
}

CoUninitialize();
}

[happydeer]

读取pack后面的那个字节的高四位，如果值为2则是mpeg1文件，如果值为4则是mpeg2文件，如下：

00 00 01 BA 21 .... -> mpeg1
00 00 01 BA 44 .... -> mpeg2