I know the video would be useful in many situations to prove someone ELSE is guilty of an infraction...
Only if the camera features GPS and G-sensor tracking, and even then it still depends on the insurance-expert (or even a judge) to accept or actually question the data & footage of that kit as legally valid evidence...
And you can be sure that the insurance-expert and/or legal protection lawyer of your opponent will start to dispute the camera data over not being an officially calibrated instrument (like speed cams/guns), etc...
So whatever that film shows must be beyond any doubt...
if 10 mins prior to that you were speeding or doing something it might be used against you and the system gets 2 for the price of 1... I don't know if that would work that way.
That would be the case if the kit gets confiscated and its content examined by law enforcement, dunno about the legal situation in the US (But methinks LEOs there have just ALL rights and can do whatever they see fit ...).
Such could happen if you're incapacitated after a crash or such...
But then again a LEO could also simply confiscate your GPS at any time to get a hold of the recorded tracks, which as well log all speeds over ground including location/roadway and time code, to cite you for violations that had happened last week or so...
Fortunately that idea hasn't rooted within the authorities... yet... ;-)
I have a go pro and use it occasionally for scenic videos.. If I commuted more I probably would find a way to video every day just-in-case I needed some evidence but around here you almost have to ride outside the limits to keep from getting run over...
A GoPro isn't much help in that as it lacks GPS tracking and G-Sensor readings... at max it has a time code... dunno if that would be sufficient to be used as legal evidence for a crash investigation...
Real dash-cams produce loops, like the last 3 minutes are being kept, overwrite protected only if you push a button or the G-sensor logs an incident, otherwise the tracks will be automatically overwritten...
They also come/feature a computer program, enabling to read the stored loops while putting the GPS info on-screen, producing a video file with location, direction, speed, etc...