Looping is a function of the playback software - it can't be defined from within a creation tool like AE.
On Mac OS, the newer Quicktime X is woefully short of features, including a loop function. Be sure to install the older Quicktime 7 player for the ability to loop and pingpong playback.
On Mac OS, the newer Quicktime X is woefully short of features
Totally agree. I hope they boss-out Quicktime X...soon.
including a loop function
Unbelievably, they actually did put in a loop function (under the View menu). No ping-pong though. :S