I would like to capture video stream using the AudioVideoCaptureDevice class.
I have written this code in the code behind associated to a page:

var resolution = AudioVideoCaptureDevice.GetAvailableCaptureResolutions(CameraSensorLocation.Back)[0];
var cam = await AudioVideoCaptureDevice.OpenAsync(CameraSensorLocation.Back, resolution);

where viewfinderBrush is a VideoBrush control located in the XAML page.

The stream is displayed on the screen, but there is not autofocus (when getting close to objects, for example ; in the contrary, the built-in camera application constantly auto focuses the lens when in video mode).
I was not able to find any sample anywhere.

Any idea ?
Thank you,