embedthumbnail option

[pauldubois98]

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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

When downloading mp3 from Youtube, the embedthumbnail option doesn't work properly: the thumbnail is only displayed with VLC, but not with other mp3 readers (as the standards Windows ones, as well and Android ones).
This is a very small issue, only some arguments when calling FFmpeg have been changed.

[Magnusmm1999]

Can confirm this fixed my issues tyvm