Since Firefox 24.0 now supports most video formats in HTML5 video tags in Linux using gstreamer, I started looking into hardware-accelerating this process. I'm an ATI user, so I'm used to having to jump through hoops. I'm an Arch user (x86_64), and I have installed: >catalyst, the proprietary ATI driver, which provides XvBA hardware-acceleration >libva-xvba-driver, the package that enables VA-API (by passing it to XvBA) >libvdpau-va-gl, which enables VDPAU (by passing it to VA-API) >gstreamer0.10-{base,good,ugly,bad}, the video playback backend that Firefox uses in Linux Yes, I did toggle media.gstreamer.enabled in about:config, before anyone asks. :P When I open an h.264 file or an MP4 file inside Firefox (or use an MP4 video on Youtube via the script ViewTube, e.g. http://www.youtube.com/watch?v=zuXTeEwr5Rs ), the video plays, but CPU usage flies to 100%. It will stay there for the whole video, unless I pause the video, wait a few seconds, and unpause it. Then CPU usage drops to something much more sane. If I download, and play the same file in mplayer (i.e. via VDPAU, via VA-API), CPU usage is noticably (but not substantially) lower than in Firefox. If I play it in VLC (i.e. just via VA-API), CPU usage is lower still. I even tried using the package >gstreamer0.10-vaapi which adds VA-API support directly to gstreamer, but CPU usage didn't change noticably, and it still uses 100% unless I pause and unpause. This ultimately leads me to my question: Is there a way to check what video-acceleration backend Firefox/gstreamer is using, or force it to use a particular one? I'm getting the sneaking suspicion that it's not using VA-API or VDPAU, and instead something like software or just OpenGL.