Syntax: --custom-meta "TAGNAME=string with optional %(format)s" Example: --custom-meta "comment=%(webpage_url)s\n%(description)s" This can be invoked multiple times for different tags. Example 2: youtube-dl --add-metadata -f 18 --meta 'artist=%(uploader_id)s' --meta 'comment=url: %(webpage_url)s\nviews: %(view_count)s / Rating: %(average_rating)s\n\n%(description)s' https://www.youtube.com/watch?v=WzhW20hLp6M (snip) [ffmpeg] Adding metadata to 'Breaking Bad Remix (Seasons 3-5)-WzhW20hLp6M.mp4' mp4info Breaking\ Bad\ Remix\ \(Seasons\ 3-5\)-WzhW20hLp6M.mp4 (snip) Artist: uploader: placeboing Comments: url: https://www.youtube.com/watch?v=WzhW20hLp6M views: 5601679 / Rating: 4.97684526443 Music and remixing by me. Seasons 1 and 2 remix: http://www.youtube.com/watch?v=WsqdmqRgrIc MP3 download: https://www.dropbox.com/s/39luqbbi5cu36du/Chris%20Lohr%20-%20Breaking%20Bad%20Remix%20seasons%203-5.mp3