[RFC] alpha-channel support for vp9
I've been trying to add support for alpha channels to the vp9enc/vp9dec plugins. In theory, this should be very straightforward, as libvpx directly supports ARGB as pixel format. However, when I build the vpx plugins with the attached patch, I can't quite get the result to actually work in a pipeline, even though gst-inspect shows that ARGB is now supported.
E.g. when I try something like
gst-launch-1.0 -m videotestsrc ! video/x-raw,framerate=15/1,width=640,height=480 ! alpha method=green ! videoconvert ! vp9enc ! matroskamux ! filesink location=test.mkv, I just get "Failed to encode frame". Maybe I'm naive and this is not nearly as simple, any hints what I might be missing?