How can I change the volume level, mute audio, or access audio as a Unity audio source?

All of the 3D WebView packages currently output audio directly to the system. I have a feature request to make it so that audio is output as a Unity audio source on platforms that can support it (likely just Windows and macOS), and I will update this page in the future when I implement that. Although 3D WebView doesn't currently have C# APIs specifically for setting the volume level, you can use IWebView.ExecuteJavaScript() to run JavaScript that sets the volume of media on the page. For example, the following code sets the volume of all media elements on the page to 25%:

webViewPrefab.WebView.ExecuteJavaScript(
  "document.querySelectorAll('video, audio').forEach(mediaElement => mediaElement.volume = 0.25)"
);

For more information about how to manipulate media elements with JavaScript, please see MDN's HTMLMediaElement documentation.