Question / Help How do i capture browser source audio

I had a smart idea for twitch streaming with overlays and stuff on console basically i stream to mixer then i take browser source and then i stream to twitch now don't say i can't do that if i become a partner and stuff i already know plus by then ill actually have money to get the proper hardware but anyway how do i capture the browser source audio i hear it in preview but when i did a test record and i can't hear the audio (MACos el captain)