For some reason, the extract command regularly disobeys the -een 6 arg that I pass it on the command line at a random point in the extraction process. It starts off good, and then at some point (usually 100-200 frames into a video) will switch to generating every frame instead of every 6th frame, creating lots of cleanup work for me.
So I wrote this little script to help automate that process. Posting here in case it helps others with similar needs.