Select one file at random from a directory of audio files then rename it to the directory above

Although I can see similar posts, I would like to select a random audio file from a folder (of any size) that could be any extension.. wav/mp3/flac/wma etc... this is what im stuck on.

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So I need to choose any audio file from the directory Library and rename it where the bat file is as random choice.(the extension). So the audio file is still in Library.