Ok, I think I located the problem.
First of all, if you want yahoo video and yahoo sports widgets to show up in the widget gallery, you have to change your country to USA. And in these widgets, the videoplayer works, as said Jeremy earlier.
Second thing, to use the videoplayer, you can specifiy the URL of the video to play in two different form :
CODE
this.player.changePlaylist([{url : "myvideo"}]);
or
CODE
this.player.changePlaylist([{urls : [{bitrate: 300, url : "myvideo"}]}]);
The first one works on the emulator with framework 1.1, and the second one works on the emulator with framework 1.2.
Our TV is using the framework 1.1 so I assumed that I should use the first piece of code. Actually I was wrong and only the second one works.
Third thing, TV seems to play only WMV9 files, and as far as I know, there is some strange things going on with different audio encodings. When using a mono audio stream, if your bitrate is lower than 64kbps you hear no sound, but if you use a stereo stream, bitrates as low as 20kbps work.
I think that a precise list of specifications on which audio/video formats are supported would be a good idea.
Thank you.