FFMpeg Compress WebM - VP9 with alpha channel

Question

I'm looking for a way compress a quicktime .mov in animation format with alpha to VP9. I've tried the following:

ffmpeg -i Elephant_01.mov -vcodec libvpx-vp9 -pix_fmt yuva444p output3.webm

but I get an incompatible pixel format... error.

any suggestions, as far as I can tell VP9 -should- support the yuva444p format. Or is there another tool that works?

Answer 1

Since 2016-07-13, it's possible to encode VP9/webm videos with alpha channel (VP9a) so the command you use here will now work (assuming you got a copy of ffmpeg compiled after that date). Nevertheless, ffmpeg will complain:

Incompatible pixel format 'yuva444p' for codec 'libvpx-vp9',
auto-selecting format 'yuva420p'

The final pixel format of the video will be yuva420p, but it will be fully functional.