Enumerate all available video devices for a given videocapture engine id
'engineId', or for the default engine, if none is given. Returns a struct array
with one slot per available device. Entries of each struct in the array are
specific to the selected capture engine, except for the entry '
DeviceIndex'
which provides a handle that you could pass to
Screen('
OpenVideoCapture',
windowPtr, deviceIndex, ...); as the 'deviceIndex' argument to select the video
device corresponding to a given slot.
The function may return an empty array if no video capture devices could be
detected.