fix: infer actual system audio clock rate

Meetingnotes.xcodeproj/project.pbxproj

@@ -276,7 +276,7 @@
 				CODE_SIGN_IDENTITY = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
 				COMBINE_HIDPI_IMAGES = YES;
-				CURRENT_PROJECT_VERSION = 38;
+				CURRENT_PROJECT_VERSION = 43;
 				DEVELOPMENT_ASSET_PATHS = "\"meetingnotes/Preview Content\"";
 				DEVELOPMENT_TEAM = G9LVHZAJNX;
 				ENABLE_HARDENED_RUNTIME = YES;
@@ -290,7 +290,7 @@
 					"@executable_path/../Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 15.0;
-				MARKETING_VERSION = 1.1.26;
+				MARKETING_VERSION = 1.1.31;
 				ONLY_ACTIVE_ARCH = NO;
 				OTHER_SWIFT_FLAGS = "$(inherited) -D ENABLE_TCC_SPI";
 				PRODUCT_BUNDLE_IDENTIFIER = net.jamesbone.meetingnotes;
@@ -312,7 +312,7 @@
 				CODE_SIGN_IDENTITY = "Apple Development";
 				CODE_SIGN_STYLE = Automatic;
 				COMBINE_HIDPI_IMAGES = YES;
-				CURRENT_PROJECT_VERSION = 38;
+				CURRENT_PROJECT_VERSION = 43;
 				DEVELOPMENT_ASSET_PATHS = "\"meetingnotes/Preview Content\"";
 				DEVELOPMENT_TEAM = G9LVHZAJNX;
 				ENABLE_HARDENED_RUNTIME = YES;
@@ -326,7 +326,7 @@
 					"@executable_path/../Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 15.0;
-				MARKETING_VERSION = 1.1.26;
+				MARKETING_VERSION = 1.1.31;
 				ONLY_ACTIVE_ARCH = YES;
 				OTHER_SWIFT_FLAGS = "$(inherited) -D ENABLE_TCC_SPI";
 				PRODUCT_BUNDLE_IDENTIFIER = net.jamesbone.meetingnotes;

meetingnotes/Managers/AudioManager.swift

@@ -20,6 +20,27 @@ private enum RecoveryTranscriptionError: LocalizedError {
     }
 }
 
+private struct SystemCaptureDiagnostics {
+    var tapAdvertisedFormat = "unavailable"
+    var aggregateInputFormat = "unavailable"
+    var selectedInputFormat = "unavailable"
+    var targetFormat = "unavailable"
+    var selectedInputSampleRate: Double?
+    var targetSampleRate: Double?
+    var inputRateInference = "unavailable"
+    var firstBufferLayout: String?
+    var callbackCount: UInt64 = 0
+    var inputFrameCount: UInt64 = 0
+    var outputFrameCount: UInt64 = 0
+    var discardedCallbackCount: UInt64 = 0
+    var firstSampleTime: Double?
+    var lastSampleTime: Double?
+    var firstHostTime: UInt64?
+    var lastHostTime: UInt64?
+    var firstCallbackAt: Date?
+    var lastCallbackAt: Date?
+}
+
 /// Captures microphone and system audio locally, then sends completed files to Coder.
 @MainActor
 final class AudioManager: NSObject, ObservableObject {
@@ -50,6 +71,7 @@ final class AudioManager: NSObject, ObservableObject {
     private var micAudioURL: URL?
     private var systemAudioURL: URL?
     private var recordingStartedAt = Date()
+    private var systemDiagnostics = SystemCaptureDiagnostics()
 
     private override init() {
         super.init()
@@ -67,6 +89,7 @@ final class AudioManager: NSObject, ObservableObject {
         sessionID = UUID()
         self.meetingID = meetingID
         recordingStartedAt = Date()
+        systemDiagnostics = SystemCaptureDiagnostics()
         do {
             try prepareAudioFiles()
             startMicrophoneTap()
@@ -79,6 +102,7 @@ final class AudioManager: NSObject, ObservableObject {
 
     func stopRecordingAndTranscribe() async -> [TranscriptChunk] {
         let completedMeetingID = meetingID
+        let completedSessionID = sessionID
         let captureStartedAt = recordingStartedAt
         let files = stopCaptureAndCloseFiles()
         isProcessing = true
@@ -86,11 +110,20 @@ final class AudioManager: NSObject, ObservableObject {
             isProcessing = false
         }
 
-        repairHalfDurationSystemWAVIfNeeded(in: files)
+        let preRepairFileSummaries = files.map(audioFileSummary)
+        let repairApplied = repairHalfDurationSystemWAVIfNeeded(in: files)
         let completedFiles = files.compactMap { $0 }
         let audioFolder = preserveAudioFiles(completedFiles, meetingID: completedMeetingID)
         let transcriptionFiles = preservedAudioFiles(files, in: audioFolder)
         lastRecoveryAudioFolderName = audioFolder?.lastPathComponent
+        writeCaptureDiagnostics(
+            sessionID: completedSessionID,
+            captureStartedAt: captureStartedAt,
+            preRepairFileSummaries: preRepairFileSummaries,
+            repairedFiles: transcriptionFiles,
+            repairApplied: repairApplied,
+            audioFolder: audioFolder
+        )
         if let mismatch = captureDurationMismatch(in: transcriptionFiles) {
             let recoveryMessage = audioFolder == nil
                 ? " The audio remains in the app's temporary folder."
@@ -405,18 +438,73 @@ final class AudioManager: NSObject, ObservableObject {
               advertisedInputFormat.sampleRate > 0 else {
             throw NSError(domain: "AudioManager", code: -1, userInfo: [NSLocalizedDescriptionKey: "Unsupported system audio format"])
         }
+        systemDiagnostics.tapAdvertisedFormat = streamDescriptionSummary(tap.tapAdvertisedStreamDescription)
+        systemDiagnostics.aggregateInputFormat = streamDescriptionSummary(tap.aggregateInputStreamDescription)
+        systemDiagnostics.targetFormat = audioFormatSummary(targetFormat)
+        systemDiagnostics.targetSampleRate = targetFormat.sampleRate
         var inputFormat: AVAudioFormat?
         var converter: AVAudioConverter?
-        try tap.run(on: tapQueue) { [weak self] _, inputData, _, _, _ in
+        var pendingBuffer: AVAudioPCMBuffer?
+        var pendingInputTime: AudioTimeStamp?
+        var pendingNow: AudioTimeStamp?
+        try tap.run(on: tapQueue) { [weak self] inNow, inputData, inInputTime, _, _ in
             guard let self else { return }
             if inputFormat == nil {
+                guard let callbackFormat = self.inputFormat(
+                    for: inputData,
+                    sampleRate: advertisedInputFormat.sampleRate
+                ),
+                let currentBuffer = self.copyAudioBuffer(from: inputData, format: callbackFormat) else {
+                    self.systemDiagnostics.discardedCallbackCount += 1
+                    return
+                }
+
+                guard let previousBuffer = pendingBuffer,
+                      let previousInputTime = pendingInputTime else {
+                    pendingBuffer = currentBuffer
+                    pendingInputTime = inInputTime.pointee
+                    pendingNow = inNow.pointee
+                    return
+                }
+
+                let selectedSampleRate = self.effectiveInputSampleRate(
+                    advertisedSampleRate: advertisedInputFormat.sampleRate,
+                    previousFrameLength: previousBuffer.frameLength,
+                    previousTimestamp: previousInputTime,
+                    currentTimestamp: inInputTime.pointee
+                )
                 inputFormat = self.inputFormat(
                     for: inputData,
-                    advertisedFormat: advertisedInputFormat
+                    sampleRate: selectedSampleRate
                 )
                 if let inputFormat {
+                    self.systemDiagnostics.selectedInputFormat = self.audioFormatSummary(inputFormat)
+                    self.systemDiagnostics.selectedInputSampleRate = inputFormat.sampleRate
                     converter = AVAudioConverter(from: inputFormat, to: targetFormat)
                 }
+
+                guard let inputFormat, let converter else { return }
+                self.processAudioBuffer(
+                    { self.copyAudioBuffer(from: previousBuffer.audioBufferList, format: inputFormat) },
+                    converter: converter,
+                    targetFormat: targetFormat,
+                    source: .system,
+                    callbackTimestamp: previousInputTime,
+                    ioTimestamp: pendingNow
+                )
+                pendingBuffer = nil
+                pendingInputTime = nil
+                pendingNow = nil
+
+                self.processAudioBuffer(
+                    { self.copyAudioBuffer(from: currentBuffer.audioBufferList, format: inputFormat) },
+                    converter: converter,
+                    targetFormat: targetFormat,
+                    source: .system,
+                    callbackTimestamp: inInputTime.pointee,
+                    ioTimestamp: inNow.pointee
+                )
+                return
             }
             guard let inputFormat, let converter else { return }
             // The tap queue is serial. Reusing the converter preserves its
@@ -425,7 +513,9 @@ final class AudioManager: NSObject, ObservableObject {
                 { self.copyAudioBuffer(from: inputData, format: inputFormat) },
                 converter: converter,
                 targetFormat: targetFormat,
-                source: .system
+                source: .system,
+                callbackTimestamp: inInputTime.pointee,
+                ioTimestamp: inNow.pointee
             )
         } invalidationHandler: { [weak self] _ in
             guard let self, self.isRecording else { return }
@@ -435,7 +525,7 @@ final class AudioManager: NSObject, ObservableObject {
 
     private func inputFormat(
         for inputData: UnsafePointer<AudioBufferList>,
-        advertisedFormat: AVAudioFormat
+        sampleRate: Double
     ) -> AVAudioFormat? {
         let buffers = UnsafeMutableAudioBufferListPointer(
             UnsafeMutablePointer(mutating: inputData)
@@ -443,38 +533,97 @@ final class AudioManager: NSObject, ObservableObject {
         let channelCount = buffers.reduce(UInt32(0)) { $0 + $1.mNumberChannels }
         guard channelCount > 0 else { return nil }
 
-        // HAL tap metadata can advertise interleaved stereo while the callback
-        // supplies one mono buffer per channel (or the reverse). Constructing a
-        // PCM buffer with that mismatched layout halves its frame count and
-        // produces 2x-speed system audio. The callback's AudioBufferList is the
-        // authoritative layout for the memory we are copying.
+        // HAL I/O proc samples use the canonical Float32 representation. The
+        // tap's stream description can advertise a different common format;
+        // using that to interpret the callback bytes can halve the frame count
+        // (for example, treating four-byte Float32 samples as eight-byte
+        // Float64 samples). The callback's AudioBufferList is authoritative for
+        // its channel layout, while its sample rate comes from the input stream.
         let isInterleaved = buffers.count == 1 && channelCount > 1
         return AVAudioFormat(
-            commonFormat: advertisedFormat.commonFormat,
-            sampleRate: advertisedFormat.sampleRate,
+            commonFormat: .pcmFormatFloat32,
+            sampleRate: sampleRate,
             channels: AVAudioChannelCount(channelCount),
             interleaved: isInterleaved
         )
     }
 
+    private func effectiveInputSampleRate(
+        advertisedSampleRate: Double,
+        previousFrameLength: AVAudioFrameCount,
+        previousTimestamp: AudioTimeStamp,
+        currentTimestamp: AudioTimeStamp
+    ) -> Double {
+        let timestampsAreValid = previousTimestamp.mFlags.contains(.sampleTimeValid)
+            && currentTimestamp.mFlags.contains(.sampleTimeValid)
+        let sampleTimeDelta = currentTimestamp.mSampleTime - previousTimestamp.mSampleTime
+        guard timestampsAreValid,
+              advertisedSampleRate > 0,
+              previousFrameLength > 0,
+              sampleTimeDelta.isFinite,
+              sampleTimeDelta > 0 else {
+            systemDiagnostics.inputRateInference = "advertised (sample timestamps unavailable)"
+            return advertisedSampleRate
+        }
+
+        let inferredSampleRate = advertisedSampleRate * Double(previousFrameLength) / sampleTimeDelta
+        let plausibleRange = (advertisedSampleRate * 0.25)...(advertisedSampleRate * 1.25)
+        guard inferredSampleRate.isFinite, plausibleRange.contains(inferredSampleRate) else {
+            systemDiagnostics.inputRateInference = String(
+                format: "advertised (invalid inference %.3f from %u frames / %.3f sample-time units)",
+                inferredSampleRate,
+                previousFrameLength,
+                sampleTimeDelta
+            )
+            return advertisedSampleRate
+        }
+
+        let commonSampleRates: [Double] = [8_000, 11_025, 12_000, 16_000, 22_050, 24_000, 32_000, 44_100, 48_000, 88_200, 96_000]
+        let selectedSampleRate = commonSampleRates
+            .min(by: { abs($0 - inferredSampleRate) < abs($1 - inferredSampleRate) })
+            .flatMap { abs($0 - inferredSampleRate) / $0 <= 0.01 ? $0 : nil }
+            ?? inferredSampleRate
+        systemDiagnostics.inputRateInference = String(
+            format: "advertised=%.3f,inferred=%.3f,selected=%.3f,previousFrames=%u,sampleTimeDelta=%.3f",
+            advertisedSampleRate,
+            inferredSampleRate,
+            selectedSampleRate,
+            previousFrameLength,
+            sampleTimeDelta
+        )
+        return selectedSampleRate
+    }
+
     private func copyAudioBuffer(
         from inputData: UnsafePointer<AudioBufferList>,
         format: AVAudioFormat
     ) -> AVAudioPCMBuffer? {
-        guard let borrowedBuffer = AVAudioPCMBuffer(
-            pcmFormat: format,
-            bufferListNoCopy: inputData,
-            deallocator: nil
-        ), borrowedBuffer.frameLength > 0,
-        let ownedBuffer = AVAudioPCMBuffer(
-            pcmFormat: format,
-            frameCapacity: borrowedBuffer.frameLength
-        ) else { return nil }
-
-        ownedBuffer.frameLength = borrowedBuffer.frameLength
         let sourceBuffers = UnsafeMutableAudioBufferListPointer(
             UnsafeMutablePointer(mutating: inputData)
         )
+        if systemDiagnostics.firstBufferLayout == nil {
+            systemDiagnostics.firstBufferLayout = sourceBuffers.enumerated().map { index, buffer in
+                "buffer\(index):channels=\(buffer.mNumberChannels),bytes=\(buffer.mDataByteSize)"
+            }.joined(separator: "; ")
+        }
+        let frameLengths = sourceBuffers.compactMap { source -> AVAudioFrameCount? in
+            let bytesPerFrame = Int(source.mNumberChannels) * MemoryLayout<Float32>.size
+            guard bytesPerFrame > 0,
+                  Int(source.mDataByteSize).isMultiple(of: bytesPerFrame) else { return nil }
+            return AVAudioFrameCount(Int(source.mDataByteSize) / bytesPerFrame)
+        }
+        guard frameLengths.count == sourceBuffers.count,
+              let frameLength = frameLengths.first,
+              frameLength > 0,
+              frameLengths.allSatisfy({ $0 == frameLength }),
+              let ownedBuffer = AVAudioPCMBuffer(
+                pcmFormat: format,
+                frameCapacity: frameLength
+              ) else { return nil }
+
+        // Set the frame count explicitly instead of asking AVAudioPCMBuffer to
+        // infer it from potentially inconsistent tap metadata.
+        ownedBuffer.frameLength = frameLength
         let destinationBuffers = UnsafeMutableAudioBufferListPointer(
             ownedBuffer.mutableAudioBufferList
         )
@@ -497,20 +646,44 @@ final class AudioManager: NSObject, ObservableObject {
         _ inputBufferProvider: () -> AVAudioPCMBuffer?,
         converter: AVAudioConverter,
         targetFormat: AVAudioFormat,
-        source: AudioSource
+        source: AudioSource,
+        callbackTimestamp: AudioTimeStamp? = nil,
+        ioTimestamp: AudioTimeStamp? = nil
     ) {
         // The system callback copies its borrowed Core Audio memory while this
         // lock prevents teardown, then conversion operates on the owned copy.
         audioFileLock.lock()
         defer { audioFileLock.unlock() }
-        guard isAcceptingAudio,
-              let inputBuffer = inputBufferProvider(),
-              inputBuffer.frameLength > 0 else { return }
+        guard isAcceptingAudio else { return }
+        if source == .system {
+            systemDiagnostics.callbackCount += 1
+            let callbackAt = Date()
+            if systemDiagnostics.firstCallbackAt == nil { systemDiagnostics.firstCallbackAt = callbackAt }
+            systemDiagnostics.lastCallbackAt = callbackAt
+            if let callbackTimestamp {
+                if systemDiagnostics.firstSampleTime == nil { systemDiagnostics.firstSampleTime = callbackTimestamp.mSampleTime }
+                systemDiagnostics.lastSampleTime = callbackTimestamp.mSampleTime
+            }
+            if let ioTimestamp {
+                if systemDiagnostics.firstHostTime == nil { systemDiagnostics.firstHostTime = ioTimestamp.mHostTime }
+                systemDiagnostics.lastHostTime = ioTimestamp.mHostTime
+            }
+        }
+        guard let inputBuffer = inputBufferProvider(), inputBuffer.frameLength > 0 else {
+            if source == .system { systemDiagnostics.discardedCallbackCount += 1 }
+            return
+        }
+        if source == .system {
+            systemDiagnostics.inputFrameCount += UInt64(inputBuffer.frameLength)
+        }
 
         updateAudioLevel(inputBuffer, source: source)
         let ratio = targetFormat.sampleRate / inputBuffer.format.sampleRate
         let capacity = max(1, AVAudioFrameCount(ceil(Double(inputBuffer.frameLength) * ratio)))
-        guard let outputBuffer = AVAudioPCMBuffer(pcmFormat: targetFormat, frameCapacity: capacity) else { return }
+        guard let outputBuffer = AVAudioPCMBuffer(pcmFormat: targetFormat, frameCapacity: capacity) else {
+            if source == .system { systemDiagnostics.discardedCallbackCount += 1 }
+            return
+        }
         var suppliedInput = false
         var conversionError: NSError?
         let status = converter.convert(to: outputBuffer, error: &conversionError) { _, outputStatus in
@@ -522,7 +695,10 @@ final class AudioManager: NSObject, ObservableObject {
             outputStatus.pointee = .haveData
             return inputBuffer
         }
-        guard status != .error, conversionError == nil, outputBuffer.frameLength > 0 else { return }
+        guard status != .error, conversionError == nil, outputBuffer.frameLength > 0 else {
+            if source == .system { systemDiagnostics.discardedCallbackCount += 1 }
+            return
+        }
 
         do {
             switch source {
@@ -530,6 +706,7 @@ final class AudioManager: NSObject, ObservableObject {
                 try micAudioFile?.write(from: outputBuffer)
             case .system:
                 try systemAudioFile?.write(from: outputBuffer)
+                systemDiagnostics.outputFrameCount += UInt64(outputBuffer.frameLength)
             }
         } catch {
             DispatchQueue.main.async { [weak self] in
@@ -623,15 +800,20 @@ final class AudioManager: NSObject, ObservableObject {
         return String(format: "mic %.1fs, system %.1fs", micDuration, systemDuration)
     }
 
-    private func repairHalfDurationSystemWAVIfNeeded(in files: [URL?]) {
+    private func repairHalfDurationSystemWAVIfNeeded(in files: [URL?]) -> Bool {
         guard files.count >= 2,
               let micDuration = audioDuration(at: files[0]),
               let systemURL = files[1],
               let systemDuration = audioDuration(at: systemURL),
               micDuration >= 60,
               systemURL.pathExtension.caseInsensitiveCompare("wav") == .orderedSame,
-              (0.48...0.52).contains(systemDuration / micDuration) else { return }
-        try? halveWAVSampleRate(at: systemURL)
+              (0.48...0.52).contains(systemDuration / micDuration) else { return false }
+        do {
+            try halveWAVSampleRate(at: systemURL)
+            return true
+        } catch {
+            return false
+        }
     }
 
     private func halveWAVSampleRate(at url: URL) throws {
@@ -697,6 +879,113 @@ final class AudioManager: NSObject, ObservableObject {
         return Double(file.length) / file.processingFormat.sampleRate
     }
 
+    private func streamDescriptionSummary(_ description: AudioStreamBasicDescription?) -> String {
+        guard let description else { return "unavailable" }
+        return String(
+            format: "sampleRate=%.3f,formatID=%u,flags=%u,bytesPerPacket=%u,framesPerPacket=%u,bytesPerFrame=%u,channels=%u,bitsPerChannel=%u",
+            description.mSampleRate,
+            description.mFormatID,
+            description.mFormatFlags,
+            description.mBytesPerPacket,
+            description.mFramesPerPacket,
+            description.mBytesPerFrame,
+            description.mChannelsPerFrame,
+            description.mBitsPerChannel
+        )
+    }
+
+    private func audioFormatSummary(_ format: AVAudioFormat) -> String {
+        "sampleRate=\(format.sampleRate),channels=\(format.channelCount),commonFormat=\(format.commonFormat.rawValue),interleaved=\(format.isInterleaved)"
+    }
+
+    private func audioFileSummary(_ url: URL?) -> String {
+        guard let url else { return "missing" }
+        guard let file = try? AVAudioFile(forReading: url), file.processingFormat.sampleRate > 0 else {
+            return "\(url.lastPathComponent):unreadable"
+        }
+        let duration = Double(file.length) / file.processingFormat.sampleRate
+        return String(
+            format: "%@:sampleRate=%.3f,channels=%u,frames=%lld,duration=%.6f",
+            url.lastPathComponent,
+            file.processingFormat.sampleRate,
+            file.processingFormat.channelCount,
+            file.length,
+            duration
+        )
+    }
+
+    private func writeCaptureDiagnostics(
+        sessionID: UUID,
+        captureStartedAt: Date,
+        preRepairFileSummaries: [String],
+        repairedFiles: [URL?],
+        repairApplied: Bool,
+        audioFolder: URL?
+    ) {
+        guard let audioFolder else { return }
+        let callbackDuration = systemDiagnostics.firstCallbackAt.flatMap { first in
+            systemDiagnostics.lastCallbackAt.map { $0.timeIntervalSince(first) }
+        }
+        let sampleTimeDelta = systemDiagnostics.firstSampleTime.flatMap { first in
+            systemDiagnostics.lastSampleTime.map { $0 - first }
+        }
+        let hostTimeDelta = systemDiagnostics.firstHostTime.flatMap { first in
+            systemDiagnostics.lastHostTime.map { $0 >= first ? $0 - first : 0 }
+        }
+        let inputFrameDuration = systemDiagnostics.selectedInputSampleRate.flatMap { sampleRate in
+            sampleRate > 0 ? Double(systemDiagnostics.inputFrameCount) / sampleRate : nil
+        }
+        let outputFrameDuration = systemDiagnostics.targetSampleRate.flatMap { sampleRate in
+            sampleRate > 0 ? Double(systemDiagnostics.outputFrameCount) / sampleRate : nil
+        }
+        let observedInputRate = callbackDuration.flatMap { duration in
+            duration > 0 ? Double(systemDiagnostics.inputFrameCount) / duration : nil
+        }
+        let preRepairMic = preRepairFileSummaries.indices.contains(0) ? preRepairFileSummaries[0] : "missing"
+        let preRepairSystem = preRepairFileSummaries.indices.contains(1) ? preRepairFileSummaries[1] : "missing"
+        let postRepairMic = repairedFiles.indices.contains(0) ? audioFileSummary(repairedFiles[0]) : "missing"
+        let postRepairSystem = repairedFiles.indices.contains(1) ? audioFileSummary(repairedFiles[1]) : "missing"
+        let callbackDurationLine = callbackDuration.map { String(format: "callbackWallDuration=%.6f", $0) } ?? "callbackWallDuration=unavailable"
+        let inputFrameDurationLine = inputFrameDuration.map { String(format: "inputFrameDurationAtSelectedRate=%.6f", $0) } ?? "inputFrameDurationAtSelectedRate=unavailable"
+        let outputFrameDurationLine = outputFrameDuration.map { String(format: "outputFrameDurationAtTargetRate=%.6f", $0) } ?? "outputFrameDurationAtTargetRate=unavailable"
+        let observedInputRateLine = observedInputRate.map { String(format: "observedInputFramesPerSecond=%.3f", $0) } ?? "observedInputFramesPerSecond=unavailable"
+        let sampleTimeDeltaLine = sampleTimeDelta.map { String(format: "sampleTimeDelta=%.6f", $0) } ?? "sampleTimeDelta=unavailable"
+        let hostTimeDeltaLine = hostTimeDelta.map { "hostTimeDelta=\($0)" } ?? "hostTimeDelta=unavailable"
+        let lines: [String] = [
+            "Meetingnotes system capture diagnostics",
+            "sessionID=\(sessionID.uuidString)",
+            "createdAt=\(ISO8601DateFormatter().string(from: Date()))",
+            String(format: "captureWallDuration=%.6f", Date().timeIntervalSince(captureStartedAt)),
+            "tapAdvertisedFormat=\(systemDiagnostics.tapAdvertisedFormat)",
+            "aggregateInputFormat=\(systemDiagnostics.aggregateInputFormat)",
+            "selectedInputFormat=\(systemDiagnostics.selectedInputFormat)",
+            "inputRateInference=\(systemDiagnostics.inputRateInference)",
+            "targetFormat=\(systemDiagnostics.targetFormat)",
+            "firstBufferLayout=\(systemDiagnostics.firstBufferLayout ?? "unavailable")",
+            "callbackCount=\(systemDiagnostics.callbackCount)",
+            "inputFrameCount=\(systemDiagnostics.inputFrameCount)",
+            "outputFrameCount=\(systemDiagnostics.outputFrameCount)",
+            "discardedCallbackCount=\(systemDiagnostics.discardedCallbackCount)",
+            callbackDurationLine,
+            inputFrameDurationLine,
+            outputFrameDurationLine,
+            observedInputRateLine,
+            sampleTimeDeltaLine,
+            hostTimeDeltaLine,
+            "repairApplied=\(repairApplied)",
+            "preRepairMic=\(preRepairMic)",
+            "preRepairSystem=\(preRepairSystem)",
+            "postRepairMic=\(postRepairMic)",
+            "postRepairSystem=\(postRepairSystem)"
+        ]
+        let diagnosticsURL = audioFolder.appendingPathComponent("audio-diagnostics-\(sessionID.uuidString).txt")
+        try? lines.joined(separator: "\n").appending("\n").write(
+            to: diagnosticsURL,
+            atomically: true,
+            encoding: .utf8
+        )
+    }
+        
     private func resetAudioLevels() {
         micAudioLevel = 0
         systemAudioLevel = 0

meetingnotes/Managers/LocalStorageManager.swift

@@ -170,11 +170,13 @@ class LocalStorageManager {
                 }
             }
 
-            for audioFile in recoveryAudioFiles(in: continuationFolder) {
-                let destination = previousFolder.appendingPathComponent(audioFile.url.lastPathComponent)
+            let recoveryFiles = recoveryAudioFiles(in: continuationFolder).map(\.url)
+                + recoveryDiagnosticFiles(in: continuationFolder)
+            for recoveryFile in recoveryFiles {
+                let destination = previousFolder.appendingPathComponent(recoveryFile.lastPathComponent)
                 if FileManager.default.fileExists(atPath: destination.path) {
                     guard FileManager.default.contentsEqual(
-                        atPath: audioFile.url.path,
+                        atPath: recoveryFile.path,
                         andPath: destination.path
                     ) else {
                         rollbackMergedAudio(copiedAudioURLs, removeFolder: createdPreviousFolder ? previousFolder : nil)
@@ -184,7 +186,7 @@ class LocalStorageManager {
                 }
 
                 do {
-                    try FileManager.default.copyItem(at: audioFile.url, to: destination)
+                    try FileManager.default.copyItem(at: recoveryFile, to: destination)
                     copiedAudioURLs.append(destination)
                 } catch {
                     rollbackMergedAudio(copiedAudioURLs, removeFolder: createdPreviousFolder ? previousFolder : nil)
@@ -206,6 +208,7 @@ class LocalStorageManager {
         merged.userNotes = mergedText(previous.userNotes, continuation.userNotes)
         merged.generatedNotes = mergedText(previous.generatedNotes, continuation.generatedNotes)
         merged.templateId = previous.templateId ?? continuation.templateId
+        merged.transcriptionError = previous.transcriptionError ?? continuation.transcriptionError
         if !recoveryAudioFiles(in: previousFolder).isEmpty {
             merged.recoveryAudioFolderName = previous.id.uuidString
         }
@@ -347,6 +350,23 @@ class LocalStorageManager {
         }
     }
 
+    private func recoveryDiagnosticFiles(in folder: URL) -> [URL] {
+        guard let files = try? FileManager.default.contentsOfDirectory(
+            at: folder,
+            includingPropertiesForKeys: [.isRegularFileKey],
+            options: [.skipsHiddenFiles]
+        ) else {
+            return []
+        }
+
+        return files.filter { url in
+            let values = try? url.resourceValues(forKeys: [.isRegularFileKey])
+            return values?.isRegularFile == true
+                && url.pathExtension.caseInsensitiveCompare("txt") == .orderedSame
+                && url.lastPathComponent.lowercased().hasPrefix("audio-diagnostics-")
+        }
+    }
+
     func findRecoveryAudioFolder(for meeting: Meeting) -> URL? {
         let canonicalName = meeting.id.uuidString
         guard meeting.recoveryAudioFolderName == nil

meetingnotes/Managers/RecordingSessionManager.swift

@@ -96,7 +96,11 @@ class RecordingSessionManager: ObservableObject {
         let chunks = await audioManager.stopRecordingAndTranscribe()
         activeRecordingTranscriptChunks = chunks
         activeRecordingTranscriptChunksUpdated = chunks
-        updateActiveMeetingTranscript(meetingId: meetingId, chunks: chunks)
+        updateActiveMeetingTranscript(
+            meetingId: meetingId,
+            chunks: chunks,
+            transcriptionError: audioManager.errorMessage
+        )
         activeMeetingId = nil
         activeRecordingTranscriptChunks = []
         return chunks
@@ -117,7 +121,11 @@ class RecordingSessionManager: ObservableObject {
         audioManager.lastRecoveryAudioFolderName
     }
     
-    private func updateActiveMeetingTranscript(meetingId: UUID, chunks: [TranscriptChunk]) {
+    private func updateActiveMeetingTranscript(
+        meetingId: UUID,
+        chunks: [TranscriptChunk],
+        transcriptionError: String? = nil
+    ) {
         // Load all meetings
         var meetings = LocalStorageManager.shared.loadMeetings()
         
@@ -127,6 +135,7 @@ class RecordingSessionManager: ObservableObject {
             if let recoveryAudioFolderName = lastRecoveryAudioFolderName {
                 meetings[index].recoveryAudioFolderName = recoveryAudioFolderName
             }
+            meetings[index].transcriptionError = transcriptionError
             
             // Save the updated meeting
             let success = LocalStorageManager.shared.saveMeeting(meetings[index])

meetingnotes/Models/Meeting.swift

@@ -99,6 +99,7 @@ struct Meeting: Codable, Identifiable, Hashable {
     var generatedNotes: String
     var templateId: UUID?  // Add property to track per-meeting template
     var recoveryAudioFolderName: String?
+    var transcriptionError: String?
     // MARK: - Data versioning
     /// Version of this Meeting record on disk. Useful for migration.
     var dataVersion: Int
@@ -113,6 +114,7 @@ struct Meeting: Codable, Identifiable, Hashable {
          generatedNotes: String = "",
          templateId: UUID? = nil,
          recoveryAudioFolderName: String? = nil,
+         transcriptionError: String? = nil,
          dataVersion: Int = Meeting.currentDataVersion) {
         self.id = id
         self.date = date
@@ -122,6 +124,7 @@ struct Meeting: Codable, Identifiable, Hashable {
         self.generatedNotes = generatedNotes
         self.templateId = templateId
         self.recoveryAudioFolderName = recoveryAudioFolderName
+        self.transcriptionError = transcriptionError
         self.dataVersion = dataVersion
     }
     

meetingnotes/ProcessTap/ProcessTap.swift

@@ -63,6 +63,10 @@ final class ProcessTap {
     @ObservationIgnored
     private(set) var tapStreamDescription: AudioStreamBasicDescription?
     @ObservationIgnored
+    private(set) var tapAdvertisedStreamDescription: AudioStreamBasicDescription?
+    @ObservationIgnored
+    private(set) var aggregateInputStreamDescription: AudioStreamBasicDescription?
+    @ObservationIgnored
     private var invalidationHandler: InvalidationHandler?
 
     @ObservationIgnored
@@ -138,11 +142,11 @@ final class ProcessTap {
             tapDescription = CATapDescription(stereoMixdownOfProcesses: [process.objectID])
             logger.debug("Configuring tap for single process objectID: \(process.objectID)")
         case .systemAudio:
-            // Keep the HAL tap's buffer layout consistent with the default
-            // output stream. AudioManager performs the stereo-to-mono mix when
-            // it converts the captured audio to the 16 kHz transcription file.
-            tapDescription = CATapDescription(stereoGlobalTapButExcludeProcesses: [])
-            logger.debug("Configuring a stereo global system audio tap.")
+            // The transcription file is mono, so ask Core Audio for a mono
+            // mixdown at the source. This avoids interpreting a stereo HAL
+            // buffer as half as many frames before the 16 kHz conversion.
+            tapDescription = CATapDescription(monoGlobalTapButExcludeProcesses: [])
+            logger.info("Configuring a mono global system audio tap.")
         }
         
         tapDescription.uuid = UUID()
@@ -249,6 +253,7 @@ final class ProcessTap {
         do {
             logger.debug("Attempting to read audio tap stream basic description for tapID #\(tapID)...")
             let advertisedDescription = try tapID.readAudioTapStreamBasicDescription()
+            self.tapAdvertisedStreamDescription = advertisedDescription
 
             // The aggregate device may adapt the tap to the active hardware's
             // sample rate. Its input stream is the format actually delivered
@@ -256,7 +261,9 @@ final class ProcessTap {
             // advertisement. Using the latter can halve the written duration
             // when, for example, a 48 kHz tap is delivered at 24 kHz.
             do {
-                self.tapStreamDescription = try aggregateDeviceID.readInputStreamBasicDescription()
+                let aggregateDescription = try aggregateDeviceID.readInputStreamBasicDescription()
+                self.aggregateInputStreamDescription = aggregateDescription
+                self.tapStreamDescription = aggregateDescription
                 logger.info("Using aggregate input stream description: \(String(describing: self.tapStreamDescription), privacy: .public); tap advertised: \(String(describing: advertisedDescription), privacy: .public)")
             } catch {
                 self.tapStreamDescription = advertisedDescription

meetingnotes/Services/CoderAPIClient.swift

@@ -30,6 +30,7 @@ enum CoderAPIError: LocalizedError {
     case missingModel(String)
     case invalidResponse
     case serviceError(Int, String)
+    case audioPreparationFailed(String, String)
 
     var errorDescription: String? {
         switch self {
@@ -43,6 +44,8 @@ enum CoderAPIError: LocalizedError {
             return "Coder returned an invalid response."
         case .serviceError(let status, let message):
             return "Coder request failed (\(status)): \(message)"
+        case .audioPreparationFailed(let filename, let message):
+            return "Could not prepare \(filename) for transcription: \(message)"
         }
     }
 }
@@ -179,7 +182,12 @@ final class CoderAPIClient {
         let selectedModel = model.trimmingCharacters(in: .whitespacesAndNewlines)
         guard !selectedModel.isEmpty else { throw CoderAPIError.missingModel("transcription") }
         let apiKey = try requiredAPIKey(KeychainHelper.shared.getCoderAPIKey() ?? "")
-        let chunks = try makeAudioChunks(from: fileURL, preserveSpeakerIdentity: diarization)
+        let chunks: [AudioChunk]
+        do {
+            chunks = try makeAudioChunks(from: fileURL, preserveSpeakerIdentity: diarization)
+        } catch {
+            throw CoderAPIError.audioPreparationFailed(fileURL.lastPathComponent, error.localizedDescription)
+        }
         defer {
             for chunk in chunks where chunk.isTemporary {
                 try? FileManager.default.removeItem(at: chunk.url)
@@ -260,13 +268,38 @@ final class CoderAPIClient {
            let size = attributes[.size] as? NSNumber {
             request.setValue(size.stringValue, forHTTPHeaderField: "Content-Length")
         }
-        let (data, response) = try await transcriptionSession.upload(for: request, fromFile: bodyURL)
+        let (data, response) = try await uploadTranscription(request: request, bodyURL: bodyURL)
         try validate(response: response, data: data)
         let decoded = try JSONDecoder().decode(TranscriptionResponse.self, from: data)
         let segments = decoded.segments ?? segments(from: decoded.words ?? [])
         return Transcription(text: decoded.text, segments: segments)
     }
 
+    private func uploadTranscription(request: URLRequest, bodyURL: URL) async throws -> (Data, URLResponse) {
+        let retryDelays: [UInt64] = [3, 10]
+        for attempt in 0...retryDelays.count {
+            do {
+                return try await transcriptionSession.upload(for: request, fromFile: bodyURL)
+            } catch {
+                guard attempt < retryDelays.count, isRetryableTranscriptionError(error) else {
+                    throw error
+                }
+                try await Task.sleep(nanoseconds: retryDelays[attempt] * 1_000_000_000)
+            }
+        }
+        throw CoderAPIError.invalidResponse
+    }
+
+    private func isRetryableTranscriptionError(_ error: Error) -> Bool {
+        guard let urlError = error as? URLError else { return false }
+        switch urlError.code {
+        case .networkConnectionLost, .cannotConnectToHost, .timedOut:
+            return true
+        default:
+            return false
+        }
+    }
+
     private func makeAudioChunks(from fileURL: URL, preserveSpeakerIdentity: Bool) throws -> [AudioChunk] {
         let input = try AVAudioFile(forReading: fileURL)
         let format = input.processingFormat

meetingnotes/ViewModels/MeetingViewModel.swift

@@ -142,13 +142,24 @@ class MeetingViewModel: ObservableObject {
             .dropFirst()
             .sink { [weak self] updatedChunks in
                 guard let self = self else { return }
-                // Only update if this meeting is the active recording
-                if recordingSessionManager.isRecordingMeeting(self.meeting.id) {
+                // Stop publishes the final chunks after capture has ended but
+                // before the active meeting is cleared.
+                if recordingSessionManager.activeMeetingId == self.meeting.id {
                     self.meeting.transcriptChunks = updatedChunks
                 }
             }
             .store(in: &cancellables)
 
+        NotificationCenter.default.publisher(for: .meetingSaved)
+            .compactMap { $0.object as? Meeting }
+            .filter { [weak self] in $0.id == self?.meeting.id }
+            .sink { [weak self] savedMeeting in
+                guard let self, !self.isDeleted, self.meeting != savedMeeting else { return }
+                self.meeting = savedMeeting
+                self.refreshRecoveryAudioFolder()
+            }
+            .store(in: &cancellables)
+        
 
         
         // Auto-save when meeting properties change
@@ -215,6 +226,7 @@ class MeetingViewModel: ObservableObject {
             let chunks = await recordingSessionManager.stopRecording()
             meeting.transcriptChunks = chunks
             meeting.recoveryAudioFolderName = recordingSessionManager.lastRecoveryAudioFolderName
+            meeting.transcriptionError = recordingSessionManager.errorMessage
             refreshRecoveryAudioFolder()
             saveMeeting()
             if !meeting.formattedTranscript.isEmpty {
@@ -238,6 +250,7 @@ class MeetingViewModel: ObservableObject {
                 )
                 meeting.transcriptChunks = chunks
                 meeting.recoveryAudioFolderName = recoveryAudioFolderURL.lastPathComponent
+                meeting.transcriptionError = nil
                 selectedTab = .transcript
 
                 guard saveMeeting() else {
@@ -247,6 +260,8 @@ class MeetingViewModel: ObservableObject {
                 await generateNotes()
             } catch {
                 errorMessage = error.localizedDescription
+                meeting.transcriptionError = error.localizedDescription
+                _ = saveMeeting()
                 print("Retry transcription failed: \(error)")
             }
         }

meetingnotes/Views/MeetingListView.swift

@@ -6,6 +6,8 @@ struct MeetingListView: View {
     @StateObject private var recordingSessionManager = RecordingSessionManager.shared
     @State private var selectedMeeting: Meeting?
     @State private var navigationPath = NavigationPath()
+    @State private var recordingFailureMessage: String?
+    @State private var failedMeetingID: UUID?
     
     var body: some View {
         NavigationSplitView {
@@ -23,6 +25,38 @@ struct MeetingListView: View {
                     .background(Color.clear)
             }
         }
+        .onReceive(recordingSessionManager.$activeMeetingId.compactMap { $0 }) { meetingID in
+            if let meeting = LocalStorageManager.shared.loadMeetings().first(where: { $0.id == meetingID }) {
+                selectedMeeting = meeting
+            }
+        }
+        .onReceive(NotificationCenter.default.publisher(for: .meetingSaved)) { notification in
+            guard let savedMeeting = notification.object as? Meeting,
+                  selectedMeeting?.id == savedMeeting.id else { return }
+            selectedMeeting = savedMeeting
+        }
+        .onReceive(recordingSessionManager.$errorMessage.compactMap { $0 }) { message in
+            failedMeetingID = recordingSessionManager.activeMeetingId
+            recordingFailureMessage = message
+        }
+        .alert("Transcription Failed", isPresented: Binding(
+            get: { recordingFailureMessage != nil },
+            set: { if !$0 { recordingFailureMessage = nil } }
+        )) {
+            if failedMeetingID != nil {
+                Button("View Meeting") {
+                    selectFailedMeeting()
+                    recordingFailureMessage = nil
+                    recordingSessionManager.errorMessage = nil
+                }
+            }
+            Button("OK") {
+                recordingFailureMessage = nil
+                recordingSessionManager.errorMessage = nil
+            }
+        } message: {
+            Text(recordingFailureMessage ?? "")
+        }
     }
     
     private var sidebarContent: some View {
@@ -161,6 +195,14 @@ struct MeetingListView: View {
             return DayGroup(day: dayString, date: date, meetings: meetings.sorted { $0.date > $1.date })
         }.sorted { $0.date > $1.date }
     }
+
+    private func selectFailedMeeting() {
+        guard let failedMeetingID,
+              let meeting = LocalStorageManager.shared.loadMeetings().first(where: { $0.id == failedMeetingID }) else {
+            return
+        }
+        selectedMeeting = meeting
+    }
 }
 
 struct DayGroup {
@@ -182,7 +224,14 @@ struct MeetingRowView: View {
                         .foregroundColor(.red)
                         .font(.headline)
                 }
-                Text(meeting.title.isEmpty ? "Untitled meeting" : meeting.title)
+                if meeting.transcriptionError != nil {
+                    Image(systemName: "exclamationmark.triangle.fill")
+                        .foregroundColor(.orange)
+                        .accessibilityLabel("Transcription failed")
+                }
+                Text(meeting.title.isEmpty
+                     ? (meeting.transcriptionError == nil ? "Untitled meeting" : "Transcription failed")
+                     : meeting.title)
                     .font(.headline)
                     .lineLimit(1)
             }
@@ -542,24 +591,52 @@ struct MeetingDetailContentView: View {
     }
     
     private var transcriptView: some View {
-        ScrollView {
-            if viewModel.meeting.collapsedTranscriptChunks.isEmpty {
-                Text("Transcript will appear here...")
-                    .frame(maxWidth: .infinity, alignment: .leading)
-                    .padding()
-                    .foregroundColor(.secondary)
-            } else {
-                LazyVStack(alignment: .leading, spacing: 4) {
-                    ForEach(viewModel.meeting.collapsedTranscriptChunks) { chunk in
-                        CollapsedTranscriptChunkView(chunk: chunk)
+        VStack(alignment: .leading, spacing: 10) {
+            if let transcriptionError = viewModel.meeting.transcriptionError {
+                HStack(alignment: .top, spacing: 10) {
+                    Image(systemName: "exclamationmark.triangle.fill")
+                        .foregroundColor(.orange)
+                    VStack(alignment: .leading, spacing: 4) {
+                        Text("Transcription failed")
+                            .font(.headline)
+                        Text(transcriptionError)
+                            .font(.caption)
+                            .foregroundColor(.secondary)
+                    }
+                    Spacer()
+                    if viewModel.recoveryAudioFolderURL != nil {
+                        Button("Retry") {
+                            viewModel.retryTranscription()
+                        }
+                        .disabled(!viewModel.canRetryTranscription)
                     }
                 }
                 .padding()
+                .background(Color.orange.opacity(0.08))
+                .cornerRadius(8)
             }
+
+            ScrollView {
+                if viewModel.meeting.collapsedTranscriptChunks.isEmpty {
+                    Text(viewModel.meeting.transcriptionError == nil
+                         ? "Transcript will appear here..."
+                         : "No transcript was produced. The recording was kept and can be retried.")
+                        .frame(maxWidth: .infinity, alignment: .leading)
+                        .padding()
+                        .foregroundColor(.secondary)
+                } else {
+                    LazyVStack(alignment: .leading, spacing: 4) {
+                        ForEach(viewModel.meeting.collapsedTranscriptChunks) { chunk in
+                            CollapsedTranscriptChunkView(chunk: chunk)
+                        }
+                    }
+                    .padding()
+                }
+            }
+            .frame(maxHeight: .infinity)
+            .background(Color.gray.opacity(0.05))
+            .cornerRadius(8)
         }
-        .frame(maxHeight: .infinity)
-        .background(Color.gray.opacity(0.05))
-        .cornerRadius(8)
     }
     
     private var enhancedNotesView: some View {