Thank you for reminding me that yt-dlp also works with youtube music (didn't think of that). I just tried to list all the available formats of a song there:
ID EXT RESOLUTION FPS CH │ FILESIZE TBR PROTO │ VCODEC VBR ACODEC ABR ASR MORE INFO
────────────────────────────────────────────────────────────────────────────────────────────────────────────────
233 mp4 audio only │ m3u8 │ audio only unknown Default
234 mp4 audio only │ m3u8 │ audio only unknown Default
599 m4a audio only 2 │ 1.05MiB 31k https │ audio only mp4a.40.5 31k 22k ultralow, m4a_dash
600 webm audio only 2 │ 1.27MiB 37k https │ audio only opus 37k 48k ultralow, webm_dash
139 m4a audio only 2 │ 1.67MiB 49k https │ audio only mp4a.40.5 49k 22k low, m4a_dash
249 webm audio only 2 │ 1.86MiB 55k https │ audio only opus 55k 48k low, webm_dash
250 webm audio only 2 │ 2.44MiB 71k https │ audio only opus 71k 48k low, webm_dash
140 m4a audio only 2 │ 4.42MiB 130k https │ audio only mp4a.40.2 130k 44k medium, m4a_dash
251 webm audio only 2 │ 4.71MiB 138k https │ audio only opus 138k 48k medium, webm_dash
Hm ... no mp3 (my car accepts mp3 only) and the bit rate is not very high. Is youtube music that bad?
Both AAC and Opus fix some of MP3's inherent design problems (like imperfect handling of short sharp transients no matter how much bitrate you throw at it), so the only reason to continue using MP3 is for compatibility with old devices.
Since downloads aren't an official part of Youtube's offering, they don't have to care about old offline-only hardware players only supporting MP3, either and anything that's modern enough to still support either a Youtube app or the website will also support either AAC or Opus.
> the bit rate is not very high
There's also a high bitrate available, but only for subscribers.
