Troubleshooting media playback

If media files stopped playing in browser windows on all qubes, yet they play in VLC, what does that suggest?

If I pick the wrong audio output device in the audio widget, then video playback stops working in any browser. The browser will show 1 or 2 frames and then display a spinning icon as if it’s buffering, I think it has to do with the browser not being able to sync the video and audio data streams.