Windows 10, Brave Version 0.67.125 Chromium: 76.0.3809.100
This is a problem which previously occurred for me on Chrome - it’s now solved with Chrome. Also works with Edge, Firefox, Vivaldi etc.
Try to play this example web page, which uses an iframe to play back a recording :
What you should see is the music score for a string quartet, in sync with an embedded soundtrack from a video on YouTube. What I get in Brave is a rotating progress wheel - but the playback never starts and the visual score never appears.