Voltage drop (stop-start) impacting car DVR/dashcam
When cranking a car engine, the battery voltage sags significantly. Real automotive electronics is designed and tested against these special brown-out conditions. One solution to this problem (except it was a bluetooth device) is given here.

The solution includes a super capacitor (100 mF) and a Schottky diode, to prevent possible back flow discharge.

While technically the diode-capactior network should be placed at 12V side (it would require less capacitance to hold the same amount of charge), the cost of 16-V supercaps is much higher (`20X) than 5-V supercups.

The other solution would be a 5-V circuit with battery backup with hold time of 20-30 seconds. It will have smaller size (a 50 - 100 mAh Li-ion battery would be enough), but electronics will be much more sophisticated and expensive.