I’d love to be able to include subtitles and captions (where available) in the video files. I’ve confirmed that Apple Podcasts supports these captions (it appears to support all the same formats the usual iOS video player does), and it’s likely that other players would support some, or many, subtitle formats in the resultant mp4 videos.

It’s possible to add something like --write-sub --write-auto-sub --embed-subs to the youtube-dl command to allow for this, which will download either the manually-supplied, or automatic captions for youtube videos.