Shorter Export Options

Currently video export are limited to 30 seconds long and some of the objects (such as fog) don't loop seamlessly. This can cause files to be too large for some of us and unnecessary processing. Would be nice to include shorter video lengths (5, 10, 15 seconds) for those of us that would rather have a smaller file than a longer loop. Also to ensure seamless transition, just cut the video at half length, duplicate and reverse the video.