First question: You use
--download-sections "*00:00-10:00"
as an option to download the first 10 minutes. The asterisk means the numbers are treated as a timestamp instead of looking for a chapter with that title.
Second question I don't know.
Well that's a game changer, because I've been using ffmpeg directly to trim the files and it's very clunky by comparison.
How to turn them square?
I don't think yt-dlp has built-in image cropping, so it's just going to download thumbnails in the resolutions provided by the server. (See the --list-thumbnails option.) To crop what you download, consider a tool like ImageMagick.
to my knowledge you can't get squares from yt-dlp. Strawberry Music Player has a feature to download and embed the cover from MusicBrainz, I usually use that (I have to correct the tags from yt-dlp most of the time anyways). I think Picard has that too, but I don't use that.
If it's free and open source and it's also software, it can be discussed here. Subcommunity of Technology.
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