I am also looking for this to be implemented. I would contribute but am not sure where to start? Does anybody have any idea of how to pull this off? Is this on the roadmap?

I investigated this issue.

The main obstruction is that OSX does not give us an API to retrieve the system audio.

The only way to do it is that we implement chrome as a virtual speaker, and user needs to set this virtual speaker as output device, then we can get the audio stream. But this way looks hacky and not suitable for chrome. 

Yeah this seems difficult. Here is a stack overflow question that summarizes the issue: http://stackoverflow.com/questions/18443621/mac-os-x-virtual-audio-driver look at the first answer.

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

Sorry for the inconvenience if the bug really should have been left as Available. If you change it back, also remove the "Hotlist-Recharge-Cold" label.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

Sorry for the inconvenience if the bug really should have been left as Available.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

 Issue 844408  has been merged into this issue.

This issue is still going on with Chrome 71