View Full Version : VMR9 video mixing with alpha

July 15, 2007, 09:29:58
I'm trying to blend a video using its alpha over an image with the workbench using VMR9

The only type of video to work so far is uncompressed, I can see the media type coming out of the 'avi splitter' is ARGB32, which seems to be what the VMR9 needs for alpha blending.

I've tried with as many codecs as I can find which support alpha, however the media type coming out of the 'avi decompressor' is RGB32 which then goes thru the 'color space converter' and comes out as ARGB32 before connecting to the VMR9.

It would seem the 'avi decompressor' isnt decompressing the alpha information. Im exporting the clips with AfterEffects with alpha channel and have tried all the following codecs huffyuv, lagarith, png, vp6 and vp7.

Is there a trick to forcing the avi decompressor to output ARGB32? Or is there a codec with decodes as ARGB32 within the graph

Image sources also don't come in with alpha information, I've tried tga's and png's.

Or would a work around be to somehow add the alpha information to the stream from another source in the graph?

Marc Cymontkowski
July 15, 2007, 12:41:27

Codecs with Alpha Channel support are very rare. We have a new version of the MontiVision MJPEG Codec which supports Alpha Channels, in case that might be an interesting option for you. Please contact support@montivision.com if you like to receive the updated filters.

Best Regards,

Marc Cymontkowski

July 15, 2007, 15:13:08
Thanks, it sounds like I'll be needing something like that

However I still think Im missing something simple, surely I should be able to get at least an image to overlay using its alpha? It has the same issue as the video.
ie. It only decodes the image as RGB32 then the color converter changes it to ARGB32 before connecting to the VMR9

The only source I can get to use its alpha is uncompressed video, whats the point of the VMR9 if thats the only source that allows alpha blending?

Marc Cymontkowski
July 15, 2007, 16:16:20
Obviously a good question to ask the MS DirectShow team. But I think they just added that feature because Direct3D supports it and didn't think too much about the actual usage. Kind of the same thing happen to us when we implemented the MV Image File Source. Nobody actually requested this feature in the beginning. But since we see growing interest, we will put it on the development list.

An alternative solution may be the new version of the MV Bitmap Overlay filter, which supports alpha channels ;-) It actually uses the VMR's alpha support if its output is connected to a VMR directly or through a color space copnverter.