How to use VP9 for encoding video with alpha channel

[Ptilopsis]

VP9 should support videos with alpha channel, and I've already set the color format to rgba and the color space to srgb. FFmpeg output and .mkv container also used. But the color format of the output video is still nv12.
When I set the encoder into png, it works correctly, so I guess it might be the problem of inner ffmpeg.

 

[koala]

Please post a screenshot of your encoder settings, because they are not written to the logfile for custom ffmpeg output.

 

[Ptilopsis]

Please post a screenshot of your encoder settings, because they are not written to the logfile for custom ffmpeg output.

 

[Suslik V]

vp9 uses very special YUVA420p planes, so no go.

 

[Suslik V]

qtrle + mov has more chances.

 

[Ptilopsis]

vp9 uses very special YUVA420p planes, so no go.

That means the color format used by vp9 is different from rgba, so it's not usable?

qtrle + mov has more chances.

Works, thx! By the way, is there any documents of this encoder? I can't find it in the ffmpeg doc.

 

[Ptilopsis]

Well, I found an embarrassing thing is that the video coded by qtrle even had a higher bitrate than png