'Seamless' loop hangs/pauses at beginning of clip I've got a short video that I'd like to export as an mp4 and use in a seamless loop.

The content of the video is very abstract so it doesn't really matter where the loop occurs/what parts of the clip are butting against each other. In practice with the same file, within editors and elsewhere, edits are always seamless.

While working within both Premiere CS6 and After Effects CS6 the clip loops seamlessly. It's when I export and view the media that the short pause/stutter is visible.

I've tried to output the video in many file formats (H.264, Quicktime, MPEG4, etc.) using various export settings. The resulting file always has a short pause at the beginning of the loop when viewed on OS X Quicktime and VLC, as well as when embedded as HTML5 video (but don't get distracted by the web component.)

An example mp4 file is embedded here: http://mechaneyes.com/vid/ . It's slight, but the video is 2 seconds long, so you'll repeatedly see the hiccup. If needed you can right click on the video and save it to view elsewhere.

Thanks in advance for any assist you can give!
Within an editor each frame is complete in itself, but in the output formats you mention, the video is almost always compressed in such a way that only certain frames (called I-frames) are complete and independent. The rest are 'difference' frames that rely on information from surrounding frames. 

At a loop point there's often a need for the player to start over, to refill its buffers and prime the engine. You can often help out by ending your segment with a I-frame. But the only sure way to replicate what you see in the editor is to output only I-frames. MJPEG is an example of a codec that always does this, but there are other codecs that can be instructed to. The downside is that the video will be considerably larger. 

Try MJPEG and see if it does what you need.