ScreenCaptureKit recording output is corrupted when captureMicrophone is true

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Hello everyone,

I'm working on a screen recording app using ScreenCaptureKit and I've hit a strange issue. My app records the screen to an .mp4 file, and everything works perfectly until the .captureMicrophone is false In this case, I get a valid, playable .mp4 file.

However, as soon as I try to enable the microphone by setting streamConfig.captureMicrophone = true, the recording seems to work, but the final .mp4 file is corrupted and cannot be played by QuickTime or any other player. This happens whether capturesAudio (app audio) is on or off.

I've already added the "Privacy - Microphone Usage Description" (NSMicrophoneUsageDescription) to my Info.plist, so I don't think it's a permissions problem.

I have my logic split into a ScreenRecorder class that manages state and a CaptureEngine that handles the SCStream. Here is how I'm configuring my SCStream:

ScreenRecorder.swift

// This is my main SCStreamConfiguration
    private var streamConfiguration: SCStreamConfiguration {
        
        var streamConfig = SCStreamConfiguration()
        
        // ... other HDR/preset config ...
        
        // These are the problem properties
        streamConfig.capturesAudio = isAudioCaptureEnabled  
        streamConfig.captureMicrophone = isMicCaptureEnabled // breaks it if true
        
        streamConfig.excludesCurrentProcessAudio = false
        streamConfig.showsCursor = false
        
        if let region = selectedRegion, let display = currentDisplay {
            // My region/frame logic (works fine)
            let regionWidth = Int(region.frame.width)
            let regionHeight = Int(region.frame.height)
            
            streamConfig.width = regionWidth * scaleFactor
            streamConfig.height = regionHeight * scaleFactor
            
            // ... (sourceRect logic) ...
        }
        
        streamConfig.pixelFormat = kCVPixelFormatType_32BGRA
        streamConfig.colorSpaceName = CGColorSpace.sRGB
        streamConfig.minimumFrameInterval = CMTime(value: 1, timescale: 60)
        
        return streamConfig
    }

And here is how I'm setting up the SCRecordingOutput that writes the file:

ScreenRecorder.swift

private func initRecordingOutput(for region: ScreenPickerManager.SelectedRegion) throws {
       
        let screeRecordingOutputURL = try RecordingWorkspace.createScreenRecordingVideoFile(
            in: workspaceURL,
            sessionIndex: sessionIndex
        )
        
        let recordingConfiguration = SCRecordingOutputConfiguration()
        recordingConfiguration.outputURL = screeRecordingOutputURL
        recordingConfiguration.outputFileType = .mp4
        recordingConfiguration.videoCodecType = .hevc
      
        let recordingOutput = SCRecordingOutput(configuration: recordingConfiguration, delegate: self)
        self.recordingOutput = recordingOutput
       
    }

Finally, my CaptureEngine adds these to the SCStream:

CaptureEngine.swift

class CaptureEngine: NSObject, @unchecked Sendable {
    
    private(set) var stream: SCStream?
    private var streamOutput: CaptureEngineStreamOutput?
    
    // ... (dispatch queues) ...

    func startCapture(configuration: SCStreamConfiguration, filter: SCContentFilter, recordingOutput: SCRecordingOutput) async throws {
        
        let streamOutput = CaptureEngineStreamOutput()
        self.streamOutput = streamOutput

        do {
            stream = SCStream(filter: filter, configuration: configuration, delegate: streamOutput)
            
            // Add outputs for raw buffers (not used for file recording)
            try stream?.addStreamOutput(streamOutput, type: .screen, sampleHandlerQueue: videoSampleBufferQueue)
            try stream?.addStreamOutput(streamOutput, type: .audio, sampleHandlerQueue: audioSampleBufferQueue)
            try stream?.addStreamOutput(streamOutput, type: .microphone, sampleHandlerQueue: micSampleBufferQueue)
            
            // Add the file recording output
            try stream?.addRecordingOutput(recordingOutput)
            
            try await stream?.startCapture()
            
        } catch {
            logger.error("Failed to start capture: \(error.localizedDescription)")
            throw error
        }
    }
    
    // ... (stopCapture, etc.) ...
}

When I had the .captureMicrophone value to be false, I get a perfect .mp4 video playable everywhere, however, when its true, I am getting corrupted video which doesn't play at all :-

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