Shoutbox

They compress the movies and resize them so they won't take that much space on their servers and to make them load faster, this however also has the side effect that the quality gets worse. Nothing you can really do about it, however they do have the High Quality settings now, that should make them a bit better, but other than that there's nothing much you can do about it except, upload them at the specified resolution, because this will cause the least amount of quality degradation.