Embed thumbnail in post-processed file, instead of refusing due to original filetype

[qwertystop]

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Description of your issue, suggested solution and other information

When downloading a video for audio extraction with cover/thumbnail embedding, youtube-dl fails to embed a cover image when the downloaded file is not mp3, m4a, or mp4, even if the extracted audio file would be.

Sample command and output:

youtube-dl -o "./newglitch/%(autonumber)s - %(title)s.%(ext)s" -f bestaudio/best --audio-format mp3 --audio-quality 0 --add-metadata --autonumber-start 181 --write-thumbnail --sleep-interval 1 --embed-thumbnail --playlist-start 1 --playlist-end 10 --playlist-reverse "https://www.youtube.com/playlist?list=PL9793A30C55CED7F6"
[youtube:playlist] PL9793A30C55CED7F6: Downloading webpage
[download] Downloading playlist: Video Game Remixes ♫
[youtube:playlist] playlist Video Game Remixes ♫: Downloading 10 videos
[download] Downloading video 1 of 10
[youtube] _hTU9u-DK1g: Downloading webpage
[youtube] _hTU9u-DK1g: Downloading video info webpage
[youtube] _hTU9u-DK1g: Extracting video information
[youtube] _hTU9u-DK1g: Downloading thumbnail ...
[youtube] _hTU9u-DK1g: Writing thumbnail to: ./newglitch/00181 - Red and Blue Lavender Town Remix v.II.jpg
[download] Sleeping 1 seconds...
[download] Destination: ./newglitch/00181 - Red and Blue Lavender Town Remix v.II.webm
[download] 100% of 4.18MiB in 00:01
[ffmpeg] Adding metadata to './newglitch/00181 - Red and Blue Lavender Town Remix v.II.webm'
ERROR: Only mp3 and m4a/mp4 are supported for thumbnail embedding for now.

In this case, the format selector bestaudio/best chose webm, and youtube-dl refuses to embed a thumbnail in webm, where the expected/useful action would be to extract the audio into the requested mp3 format, then embed the thumbnail in that.

[qwertystop]

Cancel this. I had a typo in my command; I forgot to include -x. My sincerest apologies for wasting your time.