I just finished editing an HD photo montage and decided to export it as an H.264 quicktime file. I was aiming for a high bitrate since the pictures are in motion, and I ended up with a 1080p30 file averaging roughly 20-40 mbps. I know this is extremely high, but I wanted a blu-ray quality encode. Playback on my TV via PS3 looks great, but for whatever reason, this file is bringing my 8 Core, 10 gig RAM Mac Pro to its knees. Opening the file in quicktime results in horrible stuttering playback, while VLC will start playing smoothly at first and then crash, citing "computer too slow" as a possibility for the error. I'm having a hard time believing that this machine can't playback a high bit rate H.264 file. Any ideas? Oddly enough, the activity monitor is showing only moderate usage of system resources during playback.