youtube-dl

Download methods⚑

Download only the audio⚑

youtube-dl --extract-audio [url]

Download only the audio in MP3 format⚑

youtube-dl --extract-audio --audio-format mp3 [url]

Download audio and video in custom qualities and merge to mp4⚑

youtube-dl -f 'bestvideo[ext=mp4]+bestaudio[ext=m4a]/mp4' [url]

Download subtitles⚑

To download a video along with its English subtitles in srt format, use

youtube-dl --sub-lang en --convert-subs srt --write-sub {URL}

The subtitles will be written to a separate file.

Tips⚑

Ignore errors (missing videos)⚑

--ignore-errors or -i

Parallel downloads⚑

youtube-dl --get-id {playlist_url} | xargs -I '{}' -P 5 youtube-dl 'https://youtube.com/watch?v={}'

The first command (--get-id) gets a list of video IDs in the playlist, one per line. Those IDs get piped to xargs, which calls individual instances of youtube-dl to download each video. Because we're passing -P 5 to xargs, it runs up to 5 parallel instances of youtube-dl at a time.

Reference: alexwlchan