* start messing about with different mp4 metadata extraction
* heyyooo it works
* add test cow
* move useful multierror to gtserror package
* error out if video doesn't seem to be a real mp4
* test parsing mkv in disguise as mp4
* tidy up error handling
* remove extraneous line
* update framerate formatting
* use float32 for aspect
* fixy mctesterson
