[FFmpeg-user] webm transparency in a movie filter

[MediaStream]

Hi

looking for a method to force libvpx-vp9 decoder when using movie filter.

This works well, alpha is crystal:
`ffmpeg -i udp -c:v libvpx-vp9 -i ov1.webm -filter_complex
[0:v][1:v]overlay -t 5 rtmp`

Same file, same stream, but doesn't work. Screen turns black with graphics
on top:
`ffmpeg -i udp -filter_complex
"movie=ov1.webm:s=dv[ov];[0:v][ov]overlay,zmq" -t 5 rtmp`

webm file was generated from ProRes MOV, which works well in both
scenarios, but is too huge to be properly used for a long file. movie
filter is mandatory for ZMQ to work.
If anyone know a method to enforce a VP9 decoder to decode a VP9 encoded
file in a movie filter, that would be fantastic (:


Cheers!