Non-HTML5 audio is not covered

[ppseprus]

The method document.getElementsByTagName('audio') will only return HTML5 audio, but there could be audio embedded in Flash; there's Javascript audio object and God know what else...

[mavroudisv]

This is true, and it's a known limitation of the extension. Unfortunately, it seems impossible to handle all kinds of audio sources. However, flash is being phased out, and IIRC we do filter javascript audio objects.