VDPAU existing since 2008 isn't the main thing. The main problem is that in order to have a benefit from decoding in the GPU, the frame needs to be displayed o

VDPAU existing since 2008 isn't the main thing. The main problem is that in order to have a benefit from decoding in the GPU, the frame needs to be displayed on the GPU without reading it into CPU-addressable memory. The video frame needs to participate in the compositing of the whole Web page, which means the simpler approaches that video player-only apps can used aren't really available. Rather, it's necessary to be able to treat the video frame as some kind of OpenGL surface. However, the Linux graphics drivers situation being as messy as it is, Firefox doesn't yet enable OpenGL compositing by default on Linux. So getting Firefox to composite the Web page using OpenGL by default on Linux is the big prerequisite. I don't work on graphics, so I don't really know what I'm talking about in this sentence, but I'm hopeful that Wayland will eventually force Linux into the Mac-like situation where some baseline of OpenGL support can be assumed to be available and working just because the windowing system wouldn't work otherwise. Sadly, due to LTS distros, it will take a while for various legacy configurations to get upgraded out of the ecosystem.