Clipstart provides a simple mechanism called File Actions to run scripts on selected movies. These are available under the File menu. Clipstart ships with just one, a shell script that will open movies in QuickTime Player, but you can write your own in any language that can be run as a shell script, such as Perl, Python, and even AppleScript.
The file action is sent a single parameter: the full file path for the movie to open or process.