Whenever I want some sound from a video (file or youtube), I just fire up some audio editing software (audacity, goldwave) and set the computers microphone to be "Stero Mix", which on my computer means the sound signal sent to speakers. Then I just hit record, let the video play, and finally crop the sound file & save it. I haven't got system sounds on, that could sometimes mess it

On the N900 you can use Recaller to the same effect; set it to record system sounds and play whatever it is you want to play. This way I recorded the cheat-sound from Mahjong-game for use as an incoming email alert.

The advantage of this method is that if you can play the media, you will be able to record it too without hunting for some format-specific editing software, though the disadvantage is quite obvious; you have to wait as long as it takes to play the sound you want at normal speed.