vpx_alpha: handle bitstreams with intermittent alpha content
It seems some sources set the alpha flag but don't always attach an alpha layer to each frame.
Plus fix a potential deadlock when using libavcodec as the VPx decoder.
Ref #28653
It seems some sources set the alpha flag but don't always attach an alpha layer to each frame.
Plus fix a potential deadlock when using libavcodec as the VPx decoder.
Ref #28653
VideoLAN code repository instance