The reason you can't play video files like you can play audio files is (I would imagine) simply because sound has relevance to mIRC, whereas video really doesn't. You might want a sound to play when a certain event happens in IRC, either because you're not at the computer so you'd like to alerted, or simply for aesthetic reasons. Obviously a video won't help alert you if you're not looking at the monitor, and as far as aesthetic reasons go you can't be on active on IRC and watching a video at the same time, so what's the point?
