add-metadata doesn't work when container is .webm

[Spenhouet]

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Description of your issue, suggested solution and other information

If i download music with the following command, no metadata is saved:
youtube-dl -x --audio-format "mp3" --audio-quality 0 -o "/Music/%(uploader)s/%(title)s.%(ext)s" --metadata-from-title "%(artist)s - %(title)s" --add-metadata https://www.youtube.com/watch?v=0sjR0-EG3BM

The problem is, that for --audio-quality 0 the initial container is allways .webm which can't contain metadata. Therefor the converted .mp3 also doesn't contain metadata.

A workaround is to add the following command: --format "bestaudio[ext=m4a]"

Then the metadata is saved correct in the .m4a file and therefor in the converted .mp3 file.

Searching for this problem i found multiple issues with the same or a similar problem:

• #11020
• #11047
• #9960
• #11047

Therefor i want to raise awareness to this bug and the workaround.

There is a issue with the same problem: #9730
There seems to be a fix but since 09.06.2016 there wasn't any activity. Was this bug forgotten?

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[dstftw]

Duplicate of #5594.