must be set to 'tracks-layout'
must be in the format "WIDTHxHEIGHT"
list of tracks to include in the composite video. Audio tracks require the track id. Video tracks require an id and size.
(optional) the new video's title metadata
(optional) the length of the video in seconds
(optional) set the background color to something other than black. See here for color options: https://ffmpeg.org/ffmpeg-utils.html#Color