I recently purchased the new software "Explaindio". It's main feature is to animate your scribes on top of videos, which is something I've been doing with Sparkol ever since I joined some time ago. My question or idea is... If sparkol could produce a transparent background we can do our scribes on, it would make it so much easier and faster than the steps I have to take to get that effect.
you can export your scribe as PNG sequences and the background of each PNG image will be transparent.
There is a post on our blog that explains how to do this entitled 'How to overlay video with hand-drawn animation'