by thehumungus on Sat Apr 25, 2009 9:27 pm
One important thing is that every video file actually has two (possibly three if you count audio) formats.
There's the .avi, .ogg, .mp4 .mkv whatever extension, which is the wrapper for the video stream, and then there's the video stream itself, which is in a format like DIVX, XVID, MPEG-2, or whatever.
It's complicated stuff, but you could have a .avi that wouldn't play if the stream was in a dumb format, and one that would, if the stream inside the wrapper was in a more common one.