Helge Bahmann talked about bringing multimedia and audio extensions into the X Server this morning at FOSDEM. Helge talked about this topic last year at FOSDEM, but in the past year he has made more progress in this area. No multimedia extensions are yet present in the mainline X Server, but his code is working to varying degrees based upon the situation. This code is also utilizing some existing X functionality already.
Helge's work would add support for compressed images and audio to be passed through the X protocol. By doing so, playback synchronization would be handled by the X Server and would allow for some network transparent media players.
If this code ends up entering the mainline X Server, it doesn't look like it will be committed anytime soon since there is still quite a bit of work left. The current work is very low-level with a higher-level interface still being needed, there is currently no hardware-accelerated decoding, there are severe latency problems with the X Server until that becomes multi-threaded, and an audio/image de-compressor would need to enter the X Server.
Below is Helge's X multimedia talk.