Whenever I tried watching DVDs using mplayer, FreeBSD reported some strange problems via xconsole:

acd0: FAILURE - REPORT\_KEY ILLEGAL REQUEST asc=0x6f ascq=0x04

I was quite puzzled because - upon closer investigation - some DVDs worked literally out of the box, while others did not show anything. They just kept reporting this error. Finally, it dawned on me that the region code was probably wrong (I got that idea from the T10 drafts section). Indeed, in the annex of the MMC-3 draft were some error codes:

asc=6F ascq=04: MEDIA REGION CODE IS MISMATCHED TO LOGICAL UNIT REGION

Unfortunately, I don't know a way to change the region code from FreeBSD directly (most tools do not compile because of things that are different under FreeBSD). So I rebooted with a spare live-CD of Xubuntu and armed my USB stick with regionset (FWIW, I used the RPM version).

Some minutes later, everything worked - finally. My dearest thanks to the Xubuntu and LinVDR team...