I'm having problems with playing some Youtube videos but not all of them.
I have tried using the html5 Youtube player according to this answer but that didn't work and I have issued following command:
sudo apt-get install chromium-codecs-ffmpeg-extra
according to this answer but that doesn't work either. I'm on 12.04 and use Chromium. In Midori everything works so it's no biggy but I still find it weird.
Here are some of the videos that don't work:
http://www.youtube.com/watch?v=W_OXmOEGy2E
http://www.youtube.com/watch?v=T-IKpz--YMk
And here is some that do work: