I've wanted a dash cam for years but the technology just wasn't there. In the late 90s I drove around with my JVC GR-DVM70U miniDV camcorder on a tripod lashed into my back seat. No I can have 1080p video from my cellphone mounted on a windshield mount. I have lots of video but it's pretty limited due to storage limitations I choose the highest quality because my reasoning is if something goes wrong there's no point…
With an Android phone, this might even be scriptable using something like Tasker. Set it up to automatically start the streaming application as soon as the GPS records you travelling a speed over a certain limit, say 10 mph/20 kph.