Comment 23 for bug 1424201

(In reply to Tony Houghton from comment #9)
> > You're much better off using ffmpeg
>
> Only in versions of ffmpeg that support VDPAU and VAAPI. I'd be very happy
> for Firefox to use that route to gain GPU acceleration.

This is irrelevant to what ffmpeg does, nor if it was compiled to support either vaapi or vdpau. Compiling FFmpeg with vdpau or vaapi support won't automagically make applications using ffmpeg start using hardware acceleration unfortunately.

The P in VDPAU stands for Presentation. The only way you can paint an image decoded with VDPAU is to *P*resent it directly using VDPAU. It can't be rendered the way all the other images are typically painted.
VAAPI is similar (There's also the issue that an entire generation of intel GPUs are buggy)

We do not have a VDPAU compositor (nor a OpenGL-VAAPI), so we currently have no other options but copying the decoded image out of the GPU memory into a software surface (which is exactly what the vaapi gstreamer plugin does).

Doing so almost always annihilate any benefits, as copying the image back from the GPU is typically slow (and even more so with nvidia devices)

To make things worse, at this stage, firefox on linux doesn't have hardware accelerated compositor either (OpenGL isn't enabled by default).

We won't be using FFmpeg's hwaccel layer to access vaapi or vdpau (it's only a helper)

(BTW, AMD's own XvBA is perfectly documented)