You could try playing a trailer directly in totem & see if any better. Using the prior posted link as example -
Code:
totem http://trailers.apple.com/movies/independent/upsidedown/upsidedown-tlr1_h720p.mov
(totem will leave the trailer ^ (105MB) in ~/.cache, if desired try playing it with another player after fully cached
(if & when grilo plugins are enabled then the is an apple trailer one that works fairly well