title: FFMpeg access AVFoundation usb subdevice camera on OSX Mojave
body: <p>I Have a dual USB camera for VR: two cameras, one usb connection. On linux, this appears in /dev/video0 and /dev/video1 and I can capture using ffmpeg -i /dev/video0</p>
  
  <p>On Mojave, I can see both devices in the USB hub:</p>
  
  <pre><code>USB 2.0 Hub:
  
  Product ID: 0x0101
  Vendor ID:  0x1a40  (TERMINUS TECHNOLOGY INC.)
  Version:    1.11
  Speed:  Up to 480Mb/sec
  Location ID:    0x14200000 / 8
  Current Available (mA): 500
  Current Required (mA):  100
  Extra Operating Current (mA):   0
  
      Stereo Vision 2:
  
      Product ID: 0x9901
      Vendor ID:  0x0ac8  (Z-Star Microelectronics Corporation)
      Version:    27.02
      Serial Number:  SN0099
      Speed:  Up to 480Mb/sec
      Manufacturer:   SHENZHEN RERVISION TECHNOLOGY
      Location ID:    0x14220000 / 10
      Current Available (mA): 500
      Current Required (mA):  500
      Extra Operating Current (mA):   0
  
      Stereo Vision 2:
  
      Product ID: 0x9902
      Vendor ID:  0x0ac8  (Z-Star Microelectronics Corporation)
      Version:    27.02
      Serial Number:  SN0100
      Speed:  Up to 480Mb/sec
      Manufacturer:   SHENZHEN RERVISION TECHNOLOGY
      Location ID:    0x14210000 / 9
      Current Available (mA): 500
      Current Required (mA):  500
      Extra Operating Current (mA):   0
  </code></pre>
  
  <p>But when I list devices, I can see only one [0]:</p>
  
  <pre><code>ffmpeg -f avfoundation -list_devices true -i ""
      [AVFoundation input device @ 0x7fae5b501a80] AVFoundation video devices:
      [AVFoundation input device @ 0x7fae5b501a80] [0] Stereo Vision 2
      [AVFoundation input device @ 0x7fae5b501a80] [1] FaceTime HD Camera
      [AVFoundation input device @ 0x7fae5b501a80] [2] Capture screen 0
  </code></pre>
  
  <p>capturing from this device captures from one of the cameras.</p>
  
  <p>How can I get ffmpeg to detect the second usb device as well?</p>