Macbook Pro (14") internal speakers not working

Rather suddenly today, I cannot watch videos or listen to music on internal speakers. The speakers auto-mute and the video won't play. Videos spin and won't begin playing. If I try to play audio (like Spotify), the machine freezes briefly and then auto-mutes.

Note, I can get audio via headphones, either wired or bluetooth. It is ONLY when "Macbook Pro Speakers" is selected at source that it does this.

I tried reinstalling MacOS to no avail.

Any ideas?