Usually I re-save a video to compress it, scale, apply a filter, etc using QuickTime, but when applying a filter it was a bit annoying to have only the first frame of the video shown in the preview.
Today I discovered that if you pause the video in any position, that is the frame shown in the preview panel of the exporter. While it is not a real full-video preview, at least I can see a frame I like as the preview frame.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080219154353220