I can confirm that the xv and gl video is watchable using xcompmgr over compiz. Its still buggy; it refuses to accept a transparency given by transset and if the background changes (e.g scrolling a web page behind the movie) then the video disappears (apparently replaced by the background) for a fraction of a second (much like the compiz choppyness). I wonder if the xv/gl stuff doesn't like compositing and compiz is more inclined to refresh background windows.