I did use an app called iOnRoad they even sent me a free windshield mount for my phone. It doesn't record video but will take a picture when it's senses some danger such as a sudden stop i.e. trying to avoid the car in front of you stopping.

I thought about UStream but I am lucky to get a signal even here in the capital city; GPS or cell.

Maybe a RaspberryPi, a small webcam and solar panel.