Partager via

Stream Format

  • Article
 
Microsoft DirectShow 9.0

Stream Format

Both the MSDV and the UVC driver can output two DV formats: interleaved audio-video, or video only. Interleaved audio-video is the original format from the device. The video-only format contains the same data, but the samples are marked as having no audio data. The video-only format exists mainly for compatibility with applications that use Video for Windows. For more information, see Type-1 vs. Type-2 DV AVI Files.

MSDV Driver

The MSDV driver has two output pins. The first output pin sends interleaved data, and the second output pin sends video-only data. Only one output pin can be connected at a time. To select a format, connect the appropriate output pin. You can use the IAMStreamConfig interface on the output pin to find the format.

UVC Driver

Unlike the MSDV driver, the UVC driver delivers both formats from the same pin. The default format is video-only. To select the format, use the IAMStreamConfig interface on the output pin. Call the GetStreamCaps method to enumerate the media types on the output pin. For each media type, if the major type matches the desired format, call SetFormat and pass in that media type.

Format Major type
Interleaved audio and video MEDIATYPE_Interleaved
Video only MEDIATYPE_Video

The following function sets the format based on the major type GUID.

HRESULT SetStreamFormat(IAMStreamConfig *pConfig, const GUID& majorType)
{
    if (pConfig == NULL)
    {
        return E_POINTER;
    }

    // Get the number of stream capabilities.
    int count = 0, size = 0;
    HRESULT hr = pConfig->GetNumberOfCapabilities(&count, &size);
    if (FAILED(hr))
    {
        return hr;
    }

    // Allocate memory for the stream capabilities structure.
    BYTE *pCaps = new BYTE[size];
    if (pCaps == NULL)
    {
        return E_OUTOFMEMORY;
    }
    
    // Enumerate the stream capabilities.
    bool bFoundType = false;
    for (int ix = 0; ix < count; ix++)
    {
        AM_MEDIA_TYPE *pmt;
        hr = pConfig->GetStreamCaps(ix, &pmt, pCaps);
        if (FAILED(hr))
        {
            break;
        }
        else if (pmt->majortype == majorType)
        {
            // This is the media type we want.
            bFoundType = true;
            hr = pConfig->SetFormat(pmt);
            DeleteMediaType(pmt);
            break;
        }
        DeleteMediaType(pmt);
    }
    delete [] pCaps;
    if (FAILED(hr))
    {
        return hr;
    }
    return bFoundType ? S_OK : E_FAIL;
}

The MSDV driver also supports IAMStreamConfig, so you can write code that works for both device types.

See Also