feat: Add System-Wide audio tap recording functionality

Author: wobondar

Recap/Audio/Capture/Tap/AudioTapType.swift

@@ -0,0 +1,23 @@
+import Foundation
+import AudioToolbox
+import AVFoundation
+
+protocol AudioTapType: ObservableObject {
+    var activated: Bool { get }
+    var audioLevel: Float { get }
+    var errorMessage: String? { get }
+    var tapStreamDescription: AudioStreamBasicDescription? { get }
+
+    @MainActor func activate()
+    func invalidate()
+    func run(on queue: DispatchQueue, ioBlock: @escaping AudioDeviceIOBlock,
+             invalidationHandler: @escaping (Self) -> Void) throws
+}
+
+protocol AudioTapRecorderType: ObservableObject {
+    var fileURL: URL { get }
+    var isRecording: Bool { get }
+
+    @MainActor func start() throws
+    func stop()
+}

Recap/Audio/Capture/Tap/ProcessTap.swift

@@ -7,7 +7,7 @@ extension String: @retroactive LocalizedError {
     public var errorDescription: String? { self }
 }
 
-final class ProcessTap: ObservableObject {
+final class ProcessTap: ObservableObject, AudioTapType {
     typealias InvalidationHandler = (ProcessTap) -> Void
 
     let process: AudioProcess
@@ -192,7 +192,7 @@ final class ProcessTap: ObservableObject {
     }
 }
 
-final class ProcessTapRecorder: ObservableObject {
+final class ProcessTapRecorder: ObservableObject, AudioTapRecorderType {
     let fileURL: URL
     let process: AudioProcess
     private let queue = DispatchQueue(label: "ProcessTapRecorder", qos: .userInitiated)

Recap/Audio/Capture/Tap/SystemWideTap.swift

@@ -0,0 +1,306 @@
+import SwiftUI
+import AudioToolbox
+import OSLog
+import AVFoundation
+
+final class SystemWideTap: ObservableObject, AudioTapType {
+    typealias InvalidationHandler = (SystemWideTap) -> Void
+
+    let muteWhenRunning: Bool
+    private let logger: Logger
+
+    private(set) var errorMessage: String?
+    @Published private(set) var audioLevel: Float = 0.0
+
+    fileprivate func setAudioLevel(_ level: Float) {
+        audioLevel = level
+    }
+
+    init(muteWhenRunning: Bool = false) {
+        self.muteWhenRunning = muteWhenRunning
+        self.logger = Logger(subsystem: AppConstants.Logging.subsystem, category:
+                                "\(String(describing: SystemWideTap.self))")
+    }
+
+    @ObservationIgnored
+    private var processTapID: AudioObjectID = .unknown
+    @ObservationIgnored
+    private var aggregateDeviceID = AudioObjectID.unknown
+    @ObservationIgnored
+    private var deviceProcID: AudioDeviceIOProcID?
+    @ObservationIgnored
+    private(set) var tapStreamDescription: AudioStreamBasicDescription?
+    @ObservationIgnored
+    private var invalidationHandler: InvalidationHandler?
+
+    @ObservationIgnored
+    private(set) var activated = false
+
+    @MainActor
+    func activate() {
+        guard !activated else { return }
+        activated = true
+
+        logger.debug(#function)
+
+        self.errorMessage = nil
+
+        do {
+            try prepareSystemWideTap()
+        } catch {
+            logger.error("\(error, privacy: .public)")
+            self.errorMessage = error.localizedDescription
+        }
+    }
+
+    func invalidate() {
+        guard activated else { return }
+        defer { activated = false }
+
+        logger.debug(#function)
+
+        invalidationHandler?(self)
+        self.invalidationHandler = nil
+
+        if aggregateDeviceID.isValid {
+            var err = AudioDeviceStop(aggregateDeviceID, deviceProcID)
+            if err != noErr { logger.warning("Failed to stop aggregate device: \(err, privacy: .public)") }
+
+            if let deviceProcID = deviceProcID {
+                err = AudioDeviceDestroyIOProcID(aggregateDeviceID, deviceProcID)
+                if err != noErr { logger.warning("Failed to destroy device I/O proc: \(err, privacy: .public)") }
+                self.deviceProcID = nil
+            }
+
+            err = AudioHardwareDestroyAggregateDevice(aggregateDeviceID)
+            if err != noErr {
+                logger.warning("Failed to destroy aggregate device: \(err, privacy: .public)")
+            }
+            aggregateDeviceID = .unknown
+        }
+
+        if processTapID.isValid {
+            let err = AudioHardwareDestroyProcessTap(processTapID)
+            if err != noErr {
+                logger.warning("Failed to destroy audio tap: \(err, privacy: .public)")
+            }
+            self.processTapID = .unknown
+        }
+    }
+
+    private func prepareSystemWideTap() throws {
+        errorMessage = nil
+
+        let tapDescription = CATapDescription(stereoGlobalTapButExcludeProcesses: [])
+        tapDescription.uuid = UUID()
+        tapDescription.muteBehavior = muteWhenRunning ? .mutedWhenTapped : .unmuted
+        tapDescription.name = "SystemWideAudioTap"
+        tapDescription.isPrivate = true
+        tapDescription.isExclusive = true
+
+        var tapID: AUAudioObjectID = .unknown
+        var err = AudioHardwareCreateProcessTap(tapDescription, &tapID)
+
+        guard err == noErr else {
+            errorMessage = "System-wide process tap creation failed with error \(err)"
+            return
+        }
+
+        logger.debug("Created system-wide process tap #\(tapID, privacy: .public)")
+
+        self.processTapID = tapID
+
+        let systemOutputID = try AudioDeviceID.readDefaultSystemOutputDevice()
+        let outputUID = try systemOutputID.readDeviceUID()
+        let aggregateUID = UUID().uuidString
+
+        let description: [String: Any] = [
+            kAudioAggregateDeviceNameKey: "SystemWide-Tap",
+            kAudioAggregateDeviceUIDKey: aggregateUID,
+            kAudioAggregateDeviceMainSubDeviceKey: outputUID,
+            kAudioAggregateDeviceIsPrivateKey: true,
+            kAudioAggregateDeviceIsStackedKey: false,
+            kAudioAggregateDeviceTapAutoStartKey: true,
+            kAudioAggregateDeviceSubDeviceListKey: [
+                [
+                    kAudioSubDeviceUIDKey: outputUID
+                ]
+            ],
+            kAudioAggregateDeviceTapListKey: [
+                [
+                    kAudioSubTapDriftCompensationKey: true,
+                    kAudioSubTapUIDKey: tapDescription.uuid.uuidString
+                ]
+            ]
+        ]
+
+        self.tapStreamDescription = try tapID.readAudioTapStreamBasicDescription()
+
+        aggregateDeviceID = AudioObjectID.unknown
+        err = AudioHardwareCreateAggregateDevice(description as CFDictionary, &aggregateDeviceID)
+        guard err == noErr else {
+            throw "Failed to create aggregate device: \(err)"
+        }
+
+        logger.debug("Created system-wide aggregate device #\(self.aggregateDeviceID, privacy: .public)")
+    }
+
+    func run(on queue: DispatchQueue, ioBlock: @escaping AudioDeviceIOBlock,
+             invalidationHandler: @escaping InvalidationHandler) throws {
+        assert(activated, "\(#function) called with inactive tap!")
+        assert(self.invalidationHandler == nil, "\(#function) called with tap already active!")
+
+        errorMessage = nil
+
+        logger.debug("Run system-wide tap!")
+
+        self.invalidationHandler = invalidationHandler
+
+        var err = AudioDeviceCreateIOProcIDWithBlock(&deviceProcID, aggregateDeviceID, queue, ioBlock)
+        guard err == noErr else { throw "Failed to create device I/O proc: \(err)" }
+
+        err = AudioDeviceStart(aggregateDeviceID, deviceProcID)
+        guard err == noErr else { throw "Failed to start audio device: \(err)" }
+    }
+
+    deinit {
+        invalidate()
+    }
+}
+
+final class SystemWideTapRecorder: ObservableObject, AudioTapRecorderType {
+    let fileURL: URL
+    private let queue = DispatchQueue(label: "SystemWideTapRecorder", qos: .userInitiated)
+    private let logger: Logger
+
+    @ObservationIgnored
+    private weak var _tap: SystemWideTap?
+
+    private(set) var isRecording = false
+
+    init(fileURL: URL, tap: SystemWideTap) {
+        self.fileURL = fileURL
+        self._tap = tap
+        self.logger = Logger(subsystem: AppConstants.Logging.subsystem,
+                             category: "\(String(describing: SystemWideTapRecorder.self))(\(fileURL.lastPathComponent))"
+        )
+    }
+
+    private var tap: SystemWideTap {
+        get throws {
+            guard let tap = _tap else {
+                throw AudioCaptureError.coreAudioError("System-wide tap unavailable")
+            }
+            return tap
+        }
+    }
+
+    @ObservationIgnored
+    private var currentFile: AVAudioFile?
+
+    @MainActor
+    func start() throws {
+        logger.debug(#function)
+
+        guard !isRecording else {
+            logger.warning("\(#function, privacy: .public) while already recording")
+            return
+        }
+
+        let tap = try tap
+
+        if !tap.activated {
+            tap.activate()
+        }
+
+        guard var streamDescription = tap.tapStreamDescription else {
+            throw AudioCaptureError.coreAudioError("Tap stream description not available")
+        }
+
+        guard let format = AVAudioFormat(streamDescription: &streamDescription) else {
+            throw AudioCaptureError.coreAudioError("Failed to create AVAudioFormat")
+        }
+
+        logger.info("Using system-wide audio format: \(format, privacy: .public)")
+
+        let settings: [String: Any] = [
+            AVFormatIDKey: streamDescription.mFormatID,
+            AVSampleRateKey: format.sampleRate,
+            AVNumberOfChannelsKey: format.channelCount
+        ]
+
+        let file = try AVAudioFile(forWriting: fileURL, settings: settings, commonFormat: .pcmFormatFloat32,
+                                   interleaved: format.isInterleaved)
+
+        self.currentFile = file
+
+        try tap.run(on: queue) { [weak self] _, inInputData, _, _, _ in
+            guard let self, let currentFile = self.currentFile else { return }
+            do {
+                guard let buffer = AVAudioPCMBuffer(pcmFormat: format, bufferListNoCopy: inInputData,
+                                                    deallocator: nil) else {
+                    throw "Failed to create PCM buffer"
+                }
+
+                try currentFile.write(from: buffer)
+
+                self.updateAudioLevel(from: buffer)
+            } catch {
+                logger.error("\(error, privacy: .public)")
+            }
+        } invalidationHandler: { [weak self] _ in
+            guard let self else { return }
+            handleInvalidation()
+        }
+
+        isRecording = true
+    }
+
+    func stop() {
+        do {
+            logger.debug(#function)
+
+            guard isRecording else { return }
+
+            currentFile = nil
+            isRecording = false
+
+            try tap.invalidate()
+        } catch {
+            logger.error("Stop failed: \(error, privacy: .public)")
+        }
+    }
+
+    private func handleInvalidation() {
+        guard isRecording else { return }
+        logger.debug(#function)
+    }
+
+    private func updateAudioLevel(from buffer: AVAudioPCMBuffer) {
+        guard let floatData = buffer.floatChannelData else { return }
+
+        let channelCount = Int(buffer.format.channelCount)
+        let frameLength = Int(buffer.frameLength)
+
+        var maxLevel: Float = 0.0
+
+        for channel in 0..<channelCount {
+            let channelData = floatData[channel]
+
+            var channelLevel: Float = 0.0
+            for frame in 0..<frameLength {
+                let sample = abs(channelData[frame])
+                channelLevel = max(channelLevel, sample)
+            }
+
+            maxLevel = max(maxLevel, channelLevel)
+        }
+
+        let decibels = 20 * log10(max(maxLevel, 0.00001))
+        let normalizedLevel = (decibels + 60) / 60
+
+        Task { @MainActor in
+            self._tap?.setAudioLevel(min(max(normalizedLevel, 0), 1))
+        }
+    }
+}

Recap/Audio/Models/AudioProcess.swift

@@ -6,6 +6,7 @@ struct AudioProcess: Identifiable, Hashable, Sendable {
     enum Kind: String, Sendable {
         case process
         case app
+//        case system
     }
 
     var id: pid_t
@@ -51,13 +52,15 @@ extension AudioProcess.Kind {
         switch self {
         case .process: NSWorkspace.shared.icon(for: .unixExecutable)
         case .app: NSWorkspace.shared.icon(for: .applicationBundle)
+//        case .system: NSWorkspace.shared.icon(for: .systemPreferencesPane)
         }
     }
 
     var groupTitle: String {
         switch self {
         case .process: "Processes"
         case .app: "Apps"
+//        case .system: "System"
         }
     }
 }