unable to stream videos

[ratatouille]

I am using Linux mint 14 cinnamon. I am able to stream some videos of youtube and for others it shows "Video is currenlty unavailable" (for example, http://www.youtube.com/watch?v=4-FS5GN_vFE ) even though the video is available (I am able to play it on mint 12). I am also not able to play a single video of Udacity and Coursera--and that's a bigger issue. I have tried from many browsers like firefox, chrome, chromium etc but none of them stream videos. So, I think the problem is not with the browser. I also have flash so I am not sure what's exaclty wrong.