The way output streams are normally associated with tabs is through a
group_id that is passed into the audio service when the stream is created. This group_id can be used later to mute or capture audio from a specific tab. The
group_id is assigned in the browser for each WebContents (tab) in the ForwardingAudioStreamFactory.
If you want to operate on groups of streams from the same tab in the browser, consider extending the stream group APIs in the audio service instead of plumbing knowledge of things like tabs into lower levels of the media stack.
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