Video playback terrible!

I've just bought one of the brand new MacBook Pros (March 2011) which has it's own dedicated graphics card and 8GB Ram but still I find that HD video playback within Aperture 3 is unwatchable.
It starts and stops and if it works is very jittery.
Is this just how it is in Aperture?


For what it's worth, I think the problem I was experiencing was because my video files were stored on an external hard drive connected to an Airport Extreme and I was trying to play those HD videos over wifi (which presumably isn't fast enough to stream HD video)