Windows Enhanced Video Renderer (EVR): Layer multiple 1080p Videos with transparency?

Question

I am looking for ways to layer multiple 1080p Videos with transparency on Windows in C++ and DirectX or Opengl. The videos will start at different moments in time. Ideally the videos can be blended with another render target with other game content, so the resulting video texture should contain transparent pixels.

Can this be done with EVR and hardware acceleration? Which codecs are supported? http://en.wikipedia.org/wiki/Media_Foundation mentions transparency, but does not answer my questions. It sounds as if all the videos have to start at the same time and the resulting video texture has no transparency.

TIA Christoph

Answer 1

This are my research results from around 03/14 with no definitive answer to this problem. I did not try the mentioned possibility in Media Foundation, since it sounded as if the result has no transparency.

I was able to use a second gray scale video to mask the rgb video inside a shader. This can be done with a separate video stream, but syncing is needed. Moreover it is possible to encode a video with two frames side by side, but many HW accelerated video codecs do not allow this, WMF being the exception. Performance is not great but I was able to play 3 1080p30 videos simultaneously.

On a side note, to my surprise Flash was able to play 5+ 1080p30 videos with transparency simultaneously. The flash video codec allows alpha values, but I managed only inside flash to use them.