Possible stuff to add. These are features that would either require a lot of work or be very niche.
Let me know of any wild ideas you have.
I.e. output a second contact sheet that fits a certain width.
Could be derived from the final sheet with a $ convert -geometry or re-composed from the contact sheets (so that the header doesn't get resized).
e.g. $ vcs –profile web=800 file.avi
produce file.avi.png normally and file.avi-web.png with dimensions <800x
Allow the use to give their OK to individual captures. If rejected, re-capture close to it? Or maybe capture in excess and let the user pick their preferred ones?