--get-filename shows wrong extension in combination with --extract-audio/--audio-format

[danielmarschall]

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Description

The option --get-filename does not show the final filename if it is combined with --extract-audio and/or --audio-format

Example:

youtube-dl --get-filename --extract-audio --audio-format mp3 https://www.youtube.com/watch?v=XYZ

Expected behavior

The output filename provided by --get-filename should be:
VideoTitle-XYZ.mp3

Actual behavior

But it is:
VideoTitle-XYZ.webm

[dstftw]

This is expected behavior.