DX improvement: controls being visible is important for the dev to be able to easily determine if there's an audio track available or not.

Sounds like it works on 12.3.

You can indeed try opting in to it by enabling the MacSckSystemAudioLoopbackOverride flag, but one downstream codepath regards ScreenCaptureKit as too buggy to use until 13.2, so I'm not sure it'll work in practice.

Yeah, I was playing it safe here. We can and probably should get more specific.

Wrapping between 80 and 100 chars.

I guess I'm a total markdown noob but how do I wrap a long URL link without breaking it? Whenever I try to split that big string, it breaks the link in my Markdown Preview.

Yes, links can't be wrapped. It's okay if links are longer if they are the only thing in a line.

This comment sounds like it is also needed on macOS 12: https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/flag_descriptions.cc;l=6247-6253;drc=19d14ae4a957ef0f158e3b37cc7f3c76e839ce5d

You can indeed try opting in to it by enabling the MacSckSystemAudioLoopbackOverride flag, but one downstream codepath regards ScreenCaptureKit as too buggy to use until 13.2, so I'm not sure it'll work in practice.

I honestly just need to test this on macOS 12.x to get to the bottom of it. I was erring on the side of caution here.

Would be good to be explicit about which macOS versions, if any, navigator.mediaDevices.getUserMedia() can be used on.

I seem to recall from recent testing on macOS 14.6.1 that it can't be used at all, but worth double-checking before reporting it in the docs.

I'm unaware of this. 😅

I think this is inaccurate.

Looking at how IsSystemLoopbackCaptureSupported() is implemented in Chromium, loopback capture depends on both the macOS version and the state of the MacSckSystemAudioLoopbackOverride and MacCatapSystemAudioLoopbackCapture flags (which are both disabled by default). The audio system used may be based on ScreenCaptureKit or Core Audio taps.

• 🔴 version < 12.3:
  • Loopback capture is not possible.
• 🔴 12.3 ≤ version < 13.0:
  • Loopback capture is probably not possible. Although ScreenCaptureKit is technically available from macOS 12.3, the Chromium codebase notes that it is too buggy to activate until 13.2. You can try enabling the MacSckSystemAudioLoopbackOverride flag to opt in to it, but I think it won't work in practice.
• 🔴 13.0 ≤ version < 13.2:
  • Loopback capture is probably not possible. Although the top-level IsMacSckSystemAudioLoopbackCaptureEnabled() check defaults to true for this version range (meaning that the ScreenCaptureKit implementation is enabled even without enabling the MacSckSystemAudioLoopbackOverride flag), in practice, certain downstream codepaths treat it as too buggy to activate.
• 🟢 13.2 ≤ version < 14.2:
  • Loopback capture is possible, via ScreenCaptureKit only, and is enabled by default; no flag needed.
• 🟢 14.2 ≤ version < 15.0:
  • Loopback capture is possible, via either ScreenCaptureKit or Core Audio taps. By default, it is enabled, and done via ScreenCaptureKit. However, you can opt-in to Core Audio taps instead by enabling the MacCatapSystemAudioLoopbackCapture flag (which takes precedence).
• 🟡 15.0 ≤ version:
  • Loopback capture is possible, via either ScreenCaptureKit or Core Audio taps. By default, it is disabled altogether.
    • To enable it via Core Audio taps (the preferred approach from macOS 15.0 and above), enable the MacCatapSystemAudioLoopbackCapture flag. As this flag takes precedence, it doesn't matter whether MacSckSystemAudioLoopbackOverride is enabled or disabled.
    • To enable it via ScreenCaptureKit (not recommended, due to permissions prompt issues from macOS 15.0), you must enable the MacSckSystemAudioLoopbackOverride flag and disable/omit the MacCatapSystemAudioLoopbackCapture flag.

So, in summary, to support the maximum version range of 13.2 ≤ version, you should enable the MacCatapSystemAudioLoopbackCapture flag to extend support for version ≥ 15.0.

If both the MacSckSystemAudioLoopbackOverride and MacCatapSystemAudioLoopbackCapture flags are enabled, the latter will take precedence.

I should clarify that this is just based on my analysis of the latest commit on the main branch of Chromium. It might be that things were different in previous versions of Chromium, and it might be that Electron builds Chromium with different flags (however, I find no search results for either).

Does this match your experience?

This is a great write-up, thank you. I see that there's definitely some inaccuracies that'll need to be fixed here.

Per my experience, talking strictly system audio capture (there very well could be horrible bugs related to screen capture but I haven't really tested that) — For macOS versions 13.2 through 15.5, I'm able to verify that system audio capture works great via ScreenCaptureKit, only flags that are needed are MacSckSystemAudioLoopbackOverride. System permission prompts work fine.

For testing, I've created this little NPM package to make things easy in Electron Fiddle or an example project of your choice: https://github.com/alectrocute/electron-audio-loopback/tree/main

The implementation in my package is all I've tested, so we'll want to definitely reinforce in the docs that a lot of this is still experimental.

In order to provide complete guidance, the biggest questions in my mind are:

• For 12.3 ≤ version < 13.0:
  • if you enable MacSckSystemAudioLoopbackOverride, does loopback capture work?
• For 13.0 ≤ version < 13.2:
  • without passing any flags, does loopback capture work at all?
• For 15.0 ≤ version:
  • without passing any flags, does loopback capture work at all?
  • if you enable MacCatapSystemAudioLoopbackCapture, does loopback capture work?

• For 12.3 ≤ version < 13.0:

I will report back.

• For 13.0 ≤ version < 13.2:

I will report back.

• For 15.0 ≤ version:

  • without passing any flags, does loopback capture work at all?

I can verify that without passing any flags, loopback capture does not work. No errors thrown, the getDisplayMedia audio media track just arrives in an ended state.

• if you pass MacCatapSystemAudioLoopbackCapture , does loopback capture work?

I will report back.