I had a bad hit by a car a few months ago, am starting to bike again, and would like to install as-small-as-reasonable front and rear video on my bike.

The bike I used most frequently had a dyno hub and I imagine the bike I'm building will have a similar setup.

Ideally I'd take the dyno hub output, t it off either after the headlight or before with a converter, and have the video only record (and overwrite old recordings) when the line has voltage.

I'm willing to do some small circuits to make this happen, but to me a clean install is important and not having to hit a button four times a day is critical. I want to set it up so that I just start pedaling and it starts recording, so either motion activated and powered by the hub or turned on by a rectified hub output/etc is OK.

Any help?