SharpDX camera streaming not respecting MediaType set

Question

I am trying to stream web camera to my application and while I have a workaround for various resolutions I would like to use camera capabilities to provide the image in different resolution.

My workaround at the moment is as follows (in pseudo code):

ReadSample(); //always in highest resolution

var bmp = UnpackTheFrameIntoBitmap();

if(some_different_resolution_set)
{
   bmp = ResizeImageToNewResolution(bmp);
}

DrawBitmapOnCanvas(bmp);

I found out I can iterate camera native types. I use this information to find the native type that supports the selected resolution. I then set this native type to be the current media type. This is my code (half pseudo):

var nativeType = FindNativeTypeSupportingResolution(resolution);

sourceReader.SetCurrentMediaType(0, nativeType);
sourceReader.SetStreamSelection(0, true);

while(true)
{
    var sample = sourceReader.ReadSample(0, SourceReaderControlFlags.None, out int readStreamIndex, out SourceReaderFlags readFlags, out long timestamp);
    if(sample != null)
    {
        var mediaBuffer = sample.GetBufferByIndex(0);
        var sourcePointer = mediaBuffer.Lock(out int maxLength, out int currentLength);
        
        var data = new byte[sample.TotalLength];
        Marshal.Copy(sourcePointer, data, 0, frameWidth * frameHeight * 4);
        
        /// Get this data into a bitmap.
    }
}

So what happens is that setting the native type has no effect on the frame size. For instance, my camera has the highest frame size of 1920x1080. If I set the media tpye to that which is 800x600 I will still get a sample that is actually 1920x1080.

What am I doing wrong? Why does setting media type has no effect on the sample?

Answer 1

The underlying Windows Media Foundation API definitely supports video resolution changes along with active video capture.

It happens in the straightforward way you assumed: by changing media type on the go.

Some C++ code to demostrate this: https://github.com/roman380/MediaFoundationVideoCapture/...