Here's an easy way to create a video clip from a longer video in QuickTime. Open the longer video in QuickTime Player, then use the selection indicators to select a region of the video. Then click and drag the video area to the Finder, and drop. This will create a movie clipping (which can be opened in QuickTime Player) of the selected region. The clipping will retain the original video and audio content quality and codec formats. Multiple clippings to the same directory will be numbered sequentially.
This works in the same way that you can take single frame grabs from Quick Look by pausing the video and dragging it to a Finder window, as explained in this hint.
Mac OS X Hints
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