I guess that you are trying to play a High Definicion movie on your Xbox Media Center. Thats why you are here.

Well, basically to problem is that the Xbox processor ir slow for this kind of formats. You need to find a way of redecoding the movie so it plays smooth on your black box

After some try and error I think that I found the best settings for watching HD movies on the XBMC with a really really good quality.

You will need this great APP for re-decoding the movies Media Coder

Now for the settings

Video: 3850 kb/s en XVID and file .AVI
Audio: Lame MP3 VBR in position 7, it is like 192 kb/s +/-
Picture: The same, all the movies I have downloaded are in 23.98FPS.

Results: Really really smooth y superb quality.

This are some screenshots of how the Media Coder should look like

1)

2)

3)

Also, you can go one step further and use these settings are your base, and work your way up from here, maybe you can get a better quality of your movies with different decoding options.

Let me know if you found better results.

Try it out!