Read this: What is Alternative Audio Commentary?
Summary: The alternative audio is selected using the Red Button, and you will usually be prompted by a presenter when an alternative audio stream is available. If this button is selected, when there is no current alternative audio commentary available, you may hear an odd sound effect. - www.bbc.co.uk
www.bbc.co.ukWhat is Alternative Audio Commentary?…Transcriptions done by Google Cloud Platform.
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