@type backend() ::
  :any
  | :vfw
  | :v4l
  | :v4l2
  | :firewire
  | :fireware
  | :ieee1394
  | :dc1394
  | :cmu1394
  | :qt
  | :unicap
  | :dshow
  | :pvapi
  | :openni
  | :openni_asus
  | :android
  | :xiapi
  | :avfoundation
  | :giganetix
  | :msmf
  | :winrt
  | :intelperc
  | :realsense
  | :openni2
  | :openni2_asus
  | :openni2_astra
  | :gphoto2
  | :gstreamer
  | :ffmpeg
  | :images
  | :aravis
  | :opencv_mjpeg
  | :intel_mfx
  | :xine
  | :ueye
  | :obsensor
  | pos_integer()

@type open_options() :: [{:backend, backend()}]