I use this - https://play.google.com/store/apps/details?id=com.dailyroads.v
Don't drive a single meter without it. Been using this app for over a year now; before that I used this one, which works fine as well but has fewer options https://play.google.com/store/apps/details?id=com.richardtozer.dashcam

Combine it with a Scosche Magicmount, magnetic phone holder. Very convenient and using this combination saves a lot of money and effort.

The only downside is in summer when it's very hot, keeping your phone cool (especially if you also keep the screen on for navigation - I prefer Google Maps over the in-built satnav) when the sun is shining on it can be tricky! Have to keep the airconditioning on full arctic blast on the windscreen at times to prevent my phone from overheating, then.