HDMI on MB lag in playback of mkv

I have recently hooked my MB white, 2 ghz to my Sony V5500 with a hdmi cabel and getting an output of 1080p. Now i want to play video files from my computer on my tv in full hd. But everytime i try loading a 720p video file, mkv format, it starts lagging. Not much, but enough for me to get annoyed!! Is this a hardware issue? Is my macbook not powerfull enough for this task? Please help...

display port -> DVI ->HDMI?

nope, mini dvi to hdmi(female) and then to tv.
I think its the computer thats to weak, hardware regarding. Sometimes it plays smooth other times it plays with a lag. I prob. have to clean my macbook inside or something, i dont think this should be a problem for it when it is new, but mine is about 2 years old.

the macbooks only have integrated graphics, which i'm sure is the limitation, it shouldn't have a problem playing dvd quality, but as you can see, when trying to play higher resolution files it shows it's limitations, i'm sure if you were using a macbook pro with discrete graphics chip @ 256 or 512 mb you wouldn't have a problem.