XBMC capability on a standard Xbox (Intel 733Mhz PIII CPU):
720x480p video output to 720x480p = OK! (eg not upscaled).
720x480p video output to 1024x720p = OK! (eg upscaled to 720p).
720x480p video output to 1920x1080p = OK! (eg upscaled to 1080i).
1024x720p video output to 1024x720p = FAIL! (eg native 720p).
1920x1080i video output to 1920x1080i = FAIL! (eg native 1080i). Note! All above that sais FAIL don't actualy fail to play, it's just that the Xbox CPU is to slow to decode and render the high resolution so they will play so slow (dropped frames) making it unwatchable.
Désolé pour toi, mais il semblerait que les 733 Mhz de la Xbox ne soient pas suffisants pour lire correctement du contenu HD en 720p
Bonus: la liste complète des jeux Xbox compatibles HD!