Studio Artist generates Quicktime movie files. Some programs require a '.mov' file extension to be added to the file name of a Quicktime movie file in order to be able to identify them as Quicktime movie files. If the movie file name is missing the 'mov' file extension, then those programs may not recognize your rendered movie file as a Quicktime movie file.
This is less of an issue on the mac, but is an absolute requirement on windows. If you are running Studio Artist on windows, you must name your output movie files so that they include a '.mov' file extension. For example, you could name your movie file output something like 'MyPaintAnimation.mov' .
For more information on the mechanics of how to generate movie file output using Studio Artist, check out this tutorial tip.