How to record two tracks of audio while recording video?
Is there a cable that will take a stereo output from one device and connect it to the TRRS input on an Android, enabling both audio tracks to be recorded?


No. The TRRS headset jack isn't for connecting a stero input. It's for connecting a mono input (the mic) and a stereo output (the headphones), along with some extra cleverness for inline volume and transport buttons.

I don't think the OS itself supports two audio tracks as input, but if it does, the only way will be with one of those mini-mixers that connects via USB, and a USB-On-the-Go adapter. Be sure to check with the vendor that the mixer supports Android before you buy.