At first maybe replays without sound would be enough, so only the pictures would need to be downloaded. Yes probably the replay system can be used for the spectator mode. Maybe a javascript based replay viewer can be created for viewing in browser. Some of the battle-view display code could be ported to javascript... But this sounds like a hard task. The javascript based replay playback would be better than just converting the replays into AVI files, because the size of the replay itself is very small, so only the graphics would need to be downloaded, and only once. A JS based replay could be interactive, for example, rotating the map, or changing the view height, etc. would be possible. Whereas, an AVI is not interactive, and it's much larger in size. But, converting to AVI using the current game code is probably very easy to do. Update: I seem to remember that it was possible to rotate the view in UFO2000 by 90 degrees... but maybe it's not possible currently. I'll have to check this. Update 2: I have checked, but it seems to be impossible to rotate the map in the battlescape currently. Oh well, maybe someday.