Downloads 16:9 thumbnails from YouTube Music and uses " - Topic" uploader name

[probablykasper]

Before submitting an issue make sure you have:

• I've verified and I assure that I'm running youtube-dl 2018.12.09
• At least skimmed through the README, most notably the FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones
• Checked that provided video/audio/playlist URLs (if any) are alive and playable in a browser

What is the purpose of your issue?

• Bug report, at least kind of

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Downloading from YouTube Music results in a 16:9 thumbnail and an uploader name ending with - Topic.

Here's an example where I run the command youtube-dl -x --audio-format mp3 -o '%(uploader)s.%(ext)s' --embed-thumbnail https://music.youtube.com/watch?v=uRGgWKEiOHg.
The URL's page looks like this:

This is the thumbnail that is added to the output file:

This could be fine for a YouTube URL, but in this case the URL's page does not contain this thumbnail anywhere.
Additionally, the output file ends up with the filename Diamond Eyes - Topic.mp3. Again, this might be ok for a regular YouTube URL, but in the URL there is no sign of " - Topic" being part of the uploader's name.

[ealgase]

music.youtube.com is just another client for YouTube (just like gaming.youtube.com). If you check the video at https://www.youtube.com/watch?v=uRGgWKEiOHg, you'll see that both the thumbnail and uploader are correct.

[probablykasper]

@ealgase That's why I'm saying it's fine for YouTube URLs but not YouTube Music URLs. Either way it's not good UX

[ealgase]

@SpectralKH true. The way to fix this is to make a separate extractor for YouTube music, that gets the thumbnail and artist name, then sends gets the normal YouTube extractor to get the rest of the data.