I've been rendering lossless files in after effects for a year now without any problems. Now all of a sudden when I render .mov files, the playback is frayed and jumpy... audio doesn't match, etc. I've tried rendering lower then upper fields and vise versa, and both at once. nothing works. Any ideas???
Lossless seldom play back smoothly. Lossless was never designed to. If you had smooth playback before you were lucky.
Perhaps you installed some Quicktime update that changed things with hardware acceleration. Otherwise there could be a million other things at play like access speed of your storage media and what have you. Impossible to tell without more detailed info. In any case, as Rick said, "Lossless" HD or larger files rarely ever play perfectly smooth even on beefy systems. The data rates are usually simply too high...