getTrackById() is used to retrieve a Track in Examples 1,2 of MediaStream Image Capture spec [1]. This method returns a single MediaStreamTrack not a sequence also, it requires mandatory "id" parameter to be passed to retrieve the track.

So the following line should be replaced

var videoDevice = mediaStream.getTrackById()[0];

by

var videoDevice = mediaStream.getVideoTracks()[0];

The comment line before this statement should also be modified accordingly.

[1] https://dvcs.w3.org/hg/dap/raw-file/default/media-stream-capture/ImageCapture.html