hi,
i have exactly the same problem with all kind of media players.
e.g. canola2:
youtube-vids work, converted vids an videocasts from n24.de don't

i found this:
http://talk.maemo.org/showthread.php?t=29359

did you upgrade your kernel? i installed android for n810 and i guess this used another kernel. did you install debian or android?

does anybody know if android works if i flash back kernel only?

now i try to convert the vids with other codecs using "handbreake" and try to make them run that way, i report if it's working.