Phase 1: dual-track audio capture → mixed-mono 16 kHz WAV + mic VAD
AudioRecorder captures system audio (ScreenCaptureKit) + mic (AVAudioEngine) on a single serial ioQueue, one shared monotonic t0, time-driven writers (pad gaps / trim overlaps) so tracks stay aligned, and an energy mic-VAD for 'self' spans. AudioMixer sums the aligned tracks into mixed_mono_16k.wav. SessionController drives a serialized start/stop state machine, writes the session folder + self_vad.json, exposes live level meters, and finalizes on quit. Hardening from review: ioQueue single-domain (no races), stop() never hangs (mic-first teardown + bounded stopCapture), layout-agnostic mic deep-copy, discard-only video output to keep SCStream alive, VAD lockstep on committed frames, stable signing team in project.yml, single-instance enforcement.
This commit is contained in:
Grant Gilliam
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import AVFoundation
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import ScreenCaptureKit
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import CoreMedia
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import QuartzCore
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struct RecordingResult {
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let micURL: URL
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let systemURL: URL
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let mixedURL: URL
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let duration: Double
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let selfSpans: [VADSpan]
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let t0Unix: Double
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/// Non-nil if system-audio capture stopped early (e.g. SCStream error).
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let systemNote: String?
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}
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/// Dual-track local audio capture for Phase 1.
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///
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/// - System audio via `SCStream` (`capturesAudio`); its audio handler runs on
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/// `ioQueue`. A discard-only video output runs on `screenQueue` purely to keep
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/// SCStream's frame pipeline drained (an unconsumed video queue can stall the
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/// whole stream) — frames are dropped instantly, never stored.
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/// - Mic via `AVAudioEngine` input tap: the tap deep-copies the raw buffer and
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/// hands it to `ioQueue`, where it is resampled and written.
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/// - **`ioQueue` is the single isolation domain** for the writers, VAD, both
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/// resamplers, and lifecycle flags.
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/// - One shared monotonic `t0` (`CACurrentMediaTime`). Each buffer is placed at
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/// its true `(startHost − t0)` frame (gaps padded, overlaps trimmed), so mic
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/// and system stay aligned and the mix is a straight sum.
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/// - Live peak levels are exposed via `currentLevels()` for the UI meter.
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/// - `stop()` tears the mic down first and bounds `stopCapture()` with a timeout,
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/// so a wedged stream can never block finalization. No video is written.
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final class AudioRecorder: NSObject, SCStreamDelegate, SCStreamOutput {
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private let micURL: URL
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private let systemURL: URL
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private let mixedURL: URL
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private let ioQueue = DispatchQueue(label: "xyz.ten31.audio.io")
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private let screenQueue = DispatchQueue(label: "xyz.ten31.audio.screen")
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// ioQueue-only state:
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private var t0Host: Double = 0
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private var t0Unix: Double = 0
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private var micWriter: MonoTrackWriter?
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private var systemWriter: MonoTrackWriter?
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private var vad: MicVAD?
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private var tornDown = true
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private let micResampler = Resampler()
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private let systemResampler = Resampler()
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// Cross-thread, guarded by levelLock:
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private let levelLock = NSLock()
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private var micPeak: Float = 0
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private var sysPeak: Float = 0
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private var streamStopped = false
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private var systemErrorMessage: String?
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private var engine: AVAudioEngine?
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private var stream: SCStream?
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init(micURL: URL, systemURL: URL, mixedURL: URL) {
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self.micURL = micURL
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self.systemURL = systemURL
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self.mixedURL = mixedURL
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}
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// MARK: - Lifecycle
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func start() async throws {
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let t0 = CACurrentMediaTime()
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let t0u = Date().timeIntervalSince1970
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try ioQueue.sync {
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let mic = try MonoTrackWriter(url: self.micURL)
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let sys = try MonoTrackWriter(url: self.systemURL)
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self.t0Host = t0
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self.t0Unix = t0u
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self.micWriter = mic
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self.systemWriter = sys
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self.vad = MicVAD()
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self.tornDown = false
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}
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do {
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try startMic()
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try await startSystem() // throws if Screen Recording is denied
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} catch {
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await abortStart()
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throw error
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}
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}
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func stop() async -> RecordingResult {
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// Stop the mic FIRST — always succeeds and halts mic capture immediately.
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engine?.inputNode.removeTap(onBus: 0)
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engine?.stop()
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engine = nil
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// Stop system capture WITHOUT hanging: an already-errored stream can make
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// stopCapture() block forever, so skip it if it already stopped and bound
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// it with a timeout otherwise.
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if let stream, !flag({ self.streamStopped }) {
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await Self.stopCaptureWithTimeout(stream, seconds: 3)
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}
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stream = nil
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var micFrames: Int64 = 0
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var sysFrames: Int64 = 0
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var spans: [VADSpan] = []
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var t0u: Double = 0
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ioQueue.sync {
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if let tail = micResampler.drain() {
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if (micWriter?.write(tail) ?? 0) > 0 { vad?.feed(tail) }
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}
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if let tail = systemResampler.drain() { systemWriter?.write(tail) }
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vad?.finish()
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micFrames = micWriter?.framesWritten ?? 0
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sysFrames = systemWriter?.framesWritten ?? 0
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spans = vad?.spans ?? []
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t0u = t0Unix
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tornDown = true
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micWriter = nil
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systemWriter = nil
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vad = nil
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}
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try? AudioMixer.mix(mic: micURL, system: systemURL, into: mixedURL)
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let duration = Double(max(micFrames, sysFrames)) / 16_000.0
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let note = flag { self.systemErrorMessage } as String?
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return RecordingResult(
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micURL: micURL, systemURL: systemURL, mixedURL: mixedURL,
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duration: duration, selfSpans: spans, t0Unix: t0u, systemNote: note)
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}
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private func abortStart() async {
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engine?.inputNode.removeTap(onBus: 0)
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engine?.stop()
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engine = nil
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if let stream { await Self.stopCaptureWithTimeout(stream, seconds: 3) }
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stream = nil
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ioQueue.sync {
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tornDown = true
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micWriter = nil
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systemWriter = nil
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vad = nil
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}
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}
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/// Latest peak levels (0…1) for each source; decays so a stalled source fades.
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func currentLevels() -> (mic: Float, system: Float) {
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levelLock.lock(); defer { levelLock.unlock() }
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let m = micPeak, s = sysPeak
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micPeak *= 0.55; sysPeak *= 0.55
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return (m, s)
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}
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// MARK: - Ingest (ioQueue only)
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private func ingestMic(_ buffer: AVAudioPCMBuffer, startHost: Double) {
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guard !tornDown, let writer = micWriter, let vad else { return }
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let expected = max(0, Int64(((startHost - t0Host) * 16_000).rounded()))
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if expected > writer.framesWritten {
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let padded = writer.padSilence(expected - writer.framesWritten)
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if padded > 0 { vad.feedSilence(padded) }
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}
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let startIdx = max(0, Int(writer.framesWritten - expected))
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if startIdx >= Int(buffer.frameLength) { return }
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guard let chunk = Self.trimFront(buffer, by: startIdx) else { return }
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updateLevel(chunk, isMic: true)
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if writer.write(chunk) > 0 { vad.feed(chunk) }
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}
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private func ingestSystem(_ buffer: AVAudioPCMBuffer, startHost: Double) {
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guard !tornDown, let writer = systemWriter else { return }
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let expected = max(0, Int64(((startHost - t0Host) * 16_000).rounded()))
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if expected > writer.framesWritten {
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writer.padSilence(expected - writer.framesWritten)
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}
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let startIdx = max(0, Int(writer.framesWritten - expected))
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if startIdx >= Int(buffer.frameLength) { return }
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guard let chunk = Self.trimFront(buffer, by: startIdx) else { return }
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updateLevel(chunk, isMic: false)
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writer.write(chunk)
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}
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// MARK: - Mic (AVAudioEngine)
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private func startMic() throws {
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let engine = AVAudioEngine()
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let input = engine.inputNode
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let format = input.inputFormat(forBus: 0)
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input.installTap(onBus: 0, bufferSize: 4096, format: format) { [weak self] buffer, when in
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guard let self else { return }
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let entry = CACurrentMediaTime()
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let stamped = when.isHostTimeValid ? AudioRecorder.hostSeconds(when.hostTime) : entry
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let startHost = abs(stamped - entry) < 5 ? stamped : entry
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guard let raw = AudioRecorder.copy(buffer) else { return }
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self.ioQueue.async {
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guard !self.tornDown, let resampled = self.micResampler.resample(raw) else { return }
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self.ingestMic(resampled, startHost: startHost)
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}
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}
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engine.prepare()
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try engine.start()
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self.engine = engine
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}
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// MARK: - System (ScreenCaptureKit)
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private func startSystem() async throws {
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let content = try await SCShareableContent.excludingDesktopWindows(false, onScreenWindowsOnly: false)
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guard let display = content.displays.first else {
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throw NSError(domain: "Ten31", code: 1,
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userInfo: [NSLocalizedDescriptionKey: "No display available for system-audio capture."])
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}
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let filter = SCContentFilter(display: display, excludingWindows: [])
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let config = SCStreamConfiguration()
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config.capturesAudio = true
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config.excludesCurrentProcessAudio = true
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config.sampleRate = 48_000
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config.channelCount = 2
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config.width = 2
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config.height = 2
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config.minimumFrameInterval = CMTime(value: 1, timescale: 2) // ~2 fps tiny video
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config.queueDepth = 6
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let stream = SCStream(filter: filter, configuration: config, delegate: self)
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try stream.addStreamOutput(self, type: .audio, sampleHandlerQueue: ioQueue)
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// Discard-only video consumer keeps SCStream's frame queue drained so the
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// stream stays alive; frames are dropped immediately and never stored.
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try stream.addStreamOutput(self, type: .screen, sampleHandlerQueue: screenQueue)
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try await stream.startCapture()
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self.stream = stream
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}
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func stream(_ stream: SCStream, didOutputSampleBuffer sampleBuffer: CMSampleBuffer,
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of type: SCStreamOutputType) {
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guard type == .audio else { return } // .screen frames discarded here
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guard CMSampleBufferDataIsReady(sampleBuffer),
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let pcm = Self.pcmBuffer(from: sampleBuffer),
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let resampled = systemResampler.resample(pcm) else { return }
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let entry = CACurrentMediaTime()
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let pts = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
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let stamped = pts.isValid ? pts.seconds : entry
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let startHost = abs(stamped - entry) < 5 ? stamped : entry
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ingestSystem(resampled, startHost: startHost)
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}
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func stream(_ stream: SCStream, didStopWithError error: Error) {
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levelLock.lock()
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streamStopped = true
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systemErrorMessage = error.localizedDescription
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levelLock.unlock()
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}
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// MARK: - Helpers
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private func updateLevel(_ buffer: AVAudioPCMBuffer, isMic: Bool) {
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guard let ch = buffer.floatChannelData?[0] else { return }
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var peak: Float = 0
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let n = Int(buffer.frameLength)
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var i = 0
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while i < n { let a = abs(ch[i]); if a > peak { peak = a }; i += 1 }
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levelLock.lock()
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if isMic { if peak > micPeak { micPeak = peak } }
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else { if peak > sysPeak { sysPeak = peak } }
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levelLock.unlock()
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}
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/// Read a levelLock-guarded value.
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private func flag<T>(_ body: () -> T) -> T {
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levelLock.lock(); defer { levelLock.unlock() }
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return body()
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}
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private static func stopCaptureWithTimeout(_ stream: SCStream, seconds: Double) async {
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await withTaskGroup(of: Void.self) { group in
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group.addTask { try? await stream.stopCapture() }
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group.addTask { try? await Task.sleep(nanoseconds: UInt64(seconds * 1_000_000_000)) }
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_ = await group.next() // proceed as soon as either finishes
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group.cancelAll()
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}
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}
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/// Deep-copy a PCM buffer (the engine reuses the tap buffer). Layout-agnostic.
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private static func copy(_ buffer: AVAudioPCMBuffer) -> AVAudioPCMBuffer? {
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guard buffer.frameLength > 0,
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let out = AVAudioPCMBuffer(pcmFormat: buffer.format, frameCapacity: buffer.frameLength)
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else { return nil }
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out.frameLength = buffer.frameLength
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let src = UnsafeMutableAudioBufferListPointer(UnsafeMutablePointer(mutating: buffer.audioBufferList))
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let dst = UnsafeMutableAudioBufferListPointer(out.mutableAudioBufferList)
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guard src.count == dst.count else { return nil }
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for i in 0..<src.count {
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guard let s = src[i].mData, let d = dst[i].mData else { return nil }
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memcpy(d, s, min(Int(src[i].mDataByteSize), Int(dst[i].mDataByteSize)))
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}
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return out
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}
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private static func trimFront(_ buffer: AVAudioPCMBuffer, by frames: Int) -> AVAudioPCMBuffer? {
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if frames <= 0 { return buffer }
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let total = Int(buffer.frameLength)
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guard frames < total, let src = buffer.floatChannelData?[0] else { return nil }
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let n = AVAudioFrameCount(total - frames)
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guard let out = AVAudioPCMBuffer(pcmFormat: buffer.format, frameCapacity: n),
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let dst = out.floatChannelData?[0] else { return nil }
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out.frameLength = n
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memcpy(dst, src + frames, Int(n) * MemoryLayout<Float>.size)
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return out
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}
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private static func hostSeconds(_ hostTime: UInt64) -> Double {
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var info = mach_timebase_info_data_t()
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mach_timebase_info(&info)
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return Double(hostTime) * Double(info.numer) / Double(info.denom) / 1_000_000_000.0
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}
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private static func pcmBuffer(from sampleBuffer: CMSampleBuffer) -> AVAudioPCMBuffer? {
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guard let fmtDesc = CMSampleBufferGetFormatDescription(sampleBuffer),
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let asbdPtr = CMAudioFormatDescriptionGetStreamBasicDescription(fmtDesc) else { return nil }
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var asbd = asbdPtr.pointee
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guard let format = AVAudioFormat(streamDescription: &asbd) else { return nil }
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let frames = AVAudioFrameCount(CMSampleBufferGetNumSamples(sampleBuffer))
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guard frames > 0,
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let buffer = AVAudioPCMBuffer(pcmFormat: format, frameCapacity: frames) else { return nil }
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buffer.frameLength = frames
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let status = CMSampleBufferCopyPCMDataIntoAudioBufferList(
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sampleBuffer, at: 0, frameCount: Int32(frames), into: buffer.mutableAudioBufferList)
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return status == noErr ? buffer : nil
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}
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}
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