FFMpeg access AVFoundation usb subdevice camera on OSX Mojave
I revisited this a year later. An update of ffmpeg caused both devices to be seen normally.
==> Upgrading 1 outdated package:
ffmpeg 4.1.4_2 -> 4.3.1
..
ffmpeg -f avfoundation -list_devices true -i ""
[AVFoundation indev @ 0x7f85b2e00380] AVFoundation video devices:
[AVFoundation indev @ 0x7f85b2e00380] [0] Stereo Vision 2 #2
[AVFoundation indev @ 0x7f85b2e00380] [1] Stereo Vision 2
[AVFoundation indev @ 0x7f85b2e00380] [2] FaceTime HD Camera
[AVFoundation indev @ 0x7f85b2e00380] [3] Capture screen 0