DuetCam:

With DuetCam and the release of the newest operating system from Apple, iOS 13, you’ll be able to record videos using two cameras at the same time and save it to the device, share it online or even upload it directly to Instagram Stories.

During the last Apple Event, we saw this implementation in a video from Apple using Filmic Pro. The version of Filmic Pro shown is not yet available from that developer but, if all you need is this feature, DuetCam does the trick for a lot cheaper. The developer of DuetCam, Marcel Schmitz, told me via Twitter that a near-future update will have the ability to switch between the cameras while recording.