It's an issue with Webkit. Remember surf is just a tiny wrapper on top of Webkit.
For more information, checkout http://archlinuxarm.org/forum/viewtopic.php?f=64&t=8673 Unfortunately the rpi video playback work that the Raspberry Pi foundation paid Collabra to do is for webkit1 and not webkit2. And Webkit1 is not even maintained to merge in their patches. Totally lost cause.
