There’s been confirmation that the Dreamcast Media Player by Thenesis works thanks to the creator of GypPlay, TheGypsy, on the DCDev mail list:

“Wow. Much to my own surprise, the player actually PLAYED one of those videos. Specifically:

http://killer2.dhs.org/movies/FFVIII/Disc1/ff8x127.avi

…actually decodes and displays on the DC. I guess it isn’t a hoax.
Note that the frame counter still keeps going forever — once the movie is
done, it just continues along decoding nothing forever until you rewind it to
start over.

For those interested, ff8x127.avi information:
Frames: 307
Frames Per Sec: 15.0001 (the DC does about 20 fps with it)
File Size: 1.79MB
Running Time: 20.4665 Secs.
Streams: 2 (1 video and 1 MP3 audio, although it isn’t played, of course)
Resolution: 320×224

I’m sure some other ones from there will work. Dunno why my self-encoded
OpenDivX test video didn’t work.

Just wanted to pass that along.“

LyonHrt, we salute you for providing us with this news!