Right now, where are using a GStreamer meta, that if it's available, we use it to upload efficiently, a buffer into a GL texture (bug #116042). Though, it would be also good to provide a way, if the decoder delivers an EGLImage per frame, we could bind it to the texture using glEGLImageTargetTexture2DOES. There's some work done in attachment #177424 [details]
Adding Sebastian in CC. :) That patch uses some removed/old -bad API. Does this bug still makes sense? Can the same thing be done with modern GStreamer APIs?
The modified webkitgtk+ for rpi contains a patch for handling EGLImages in the composited video: http://www.raspberrypi.org/archives/5535
I think we can close this now, the long term plan here is to use glimagesink which handles already EGLImages. Feel free to reopen if you want the soon-to-be-deprecated webkitsink to handle EGLImages :)