There seems to be a lot of posts here on multimedia formats recently, so I thought I'd toss this <img src=/S/free.gif border=0 alt=free width=30 height=15> one into the mix:

"SUPER Simplified Universal Player Encoder & Renderer.
A GUI to ffmpeg, MEncoder, mplayer, x264, mppenc, ffmpeg2theora & the theora/vorbis RealProducer plugIn.

If you need a simple, yet very efficient tool to convert (encode) or play any Multimedia file, without reading manuals or spending long hours training, then SUPER is all you need. It is a Multimedia Encoder and a Multimedia Player, easy-to-use with 1 simple click.
"

I've had mostly good results from it, but due to the plethora and complexity of multimedia formats, YMMV. It's a big 25MB download because it comes with all the required codecs built in. Also, actually getting to the download mirrors can be a pain <img src=/S/groan.gif border=0 alt=groan width=16 height=15>. The actual links* are:

http://updat4.free.fr/6AB90A1AB96C06...SUPERsetup.exe
http://gpl.download.free.fr/6AB90A1AB96C06.../SUPERsetup.exe
http://updat.free.fr/6AB90A1AB96C06A...SUPERsetup.exe
http://super.free.free.fr/6AB90A1AB96C06AB.../SUPERsetup.exe

* I've left them as plain text to avoid accidental "multiclicking"

Alan