On iOS, SCStreamConfiguration.excludesCurrentProcessAudio appears to do nothing. Audio produced by our own process is captured at full level, so there is currently no way to capture device audio while excluding what our app is playing.
Measurement (deterministic probe, 2026-08-08):
Our app plays a 1 kHz tone at -4.9 dBFS RMS from its own process while capturing device audio with SCStreamConfiguration.capturesAudio = true and excludesCurrentProcessAudio = true. The configuration in force is read back from the stream and logged, so we know the flag is actually set.
The captured audio contained our own tone at -4.9 dBFS peak. Separation = 0.0 dB. 1,573 audio sample buffers analyzed over 31.5 s (16 kHz mono, 50 buffers/s), zero analysis failures, and the run was reproduced twice about 3 hours apart with byte-identical verdicts. Environment for that run: iPhone 16 Pro (iPhone17,1), iOS 27.0, built with Xcode 27 beta 4 (27A5228h) against the iOS 27 SDK, installed directly from Xcode.
Still reproducing on the current build: on iOS 27.0 (24A5418b) our shipping capture path still receives our own playback. In production we now have to cancel it ourselves - we align our playback buffer to the captured stream by cross-correlation and subtract it. The correlation between the captured signal and our own playback sits at |r| = 0.65-0.85 in the affected segments, i.e. the capture is dominated by a copy of our own output, exactly what excludesCurrentProcessAudio is supposed to remove. Doing this subtraction in-process costs real CPU and only works while we can hold a delay lock.
Why this is blocking:
RPSampleBufferType.audioApp is deprecated as of iOS 27 and the documentation points to ScreenCaptureKit as the replacement. With excludesCurrentProcessAudio non-functional there is no supported path on iOS to capture device audio while excluding one's own process. Our app is a real-time dubbing app - it captures foreign-language audio, transcribes it, and plays back a translated voice - so our own output re-entering the capture is fed straight back into transcription and corrupts the session.
My questions:
(1) Is excludesCurrentProcessAudio expected to be functional on iOS 27, or is it macOS-only in practice? The documentation does not mark it as unavailable on iOS. (2) If it is expected to work, is there anything the app must do besides setting it on the SCStreamConfiguration used to start the stream? (3) If it is not going to work on iOS, what is the supported way to exclude the current process's audio from a ScreenCaptureKit capture, now that RPSampleBufferType.audioApp is deprecated?
Filed as FB24170972 on 2026-08-08, with the full JSON event logs from both probe runs attached. There has been no response on the Feedback, which is why I am raising it here.
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