update readme

Package.swift

@@ -9,6 +9,10 @@ let package = Package(
         .macOS("14.2")
     ],
     targets: [
-        .executableTarget(name: "audiotee")
+        .executableTarget(
+            name: "audiotee",
+            swiftSettings: [
+                .define("ENABLE_TCC_SPI")
+            ])
     ]
 )

README.md

@@ -1,19 +1,10 @@
 # AudioTee
 
-**⚠️ API Instability Warning: The AudioTee API is unstable at present and subject to change without notice.**
+AudioTee captures your Mac's system audio output and writes it in PCM encoded chunks to `stdout` at regular intervals, either in base64-encoded JSON (good for humans, easy on terminals) or binary (good for other programs). It uses the [Core Audio taps](https://developer.apple.com/documentation/coreaudio/capturing-system-audio-with-core-audio-taps) API introduced in macOS 14.2 (released in December 2023). You can do whatever you want with this audio - stream it somewhere else, save it to disk, visualize it, etc.
 
-AudioTee captures your Mac's system audio output and writes it in PCM encoded chunks to `stdout` at regular intervals. All logging and metadata information is written to `stderr`, meaning at its simplest you can
+By default, it taps the audio output from **all** running process and selects the most appropriate audio chunk output format to use based on the presence of a tty. Tap output is forced to `mono` (not yet configurable) and preserves your output device's sample rate (configurable via the `--sample-rate` flag). Only the default output device is currently supported.
-capture system audio to a file like this:
 
-```bash
+My original (and so far only) use case is streaming audio to a parent process which communicates with a realtime ASR service, so AudioTee makes some design decisions you might not agree with. Open an issue or a PR and we can talk about them. I'm also no Swift developer, so contributions improving codebase idioms and general hygiene are welcome.
-/path/to/audiotee > output.pcm
-```
-
-System audio is captured using the [Core Audio taps](https://developer.apple.com/documentation/coreaudio/capturing-system-audio-with-core-audio-taps) API introduced in macOS 14.2 (released in December 2023). You can do whatever you want with this audio - stream it somewhere else, save it to disk, visualise it, etc.
-
-By default, audiotee captures audio output from **all** running processes. Tap output is forced to `mono` (not yet configurable) and preserves your output device's sample rate (configurable via the `--sample-rate` flag). Only the default output device is currently supported.
-
-My original (and so far only) use case is streaming audio to a parent process which communicates with a realtime ASR service, so AudioTee makes some design decisions you might not agree with. Open an issue or a PR and we can talk about them. I'm also no Swift developer, so contributions improving codebase idioms and general hygiene are welcome. I have internal variations (and, franky, improvements) of audiotee which allow recording mic input as well as system audio, and I'm open to making that part of the main API.
 
 Recording system audio is harder than it should be on macOS, and folks often wrestle with outdated advice and poorly documented APIs. It's a boring problem which stands in the way of lots of fun applications. There's more code here than you need to solve this problem yourself: the main classes of interest are probably [`Core/AudioTapManager`](https://github.com/makeusabrew/audiotee/blob/main/Sources/Core/AudioTapManager.swift) and [`Core/AudioRecorder`](https://github.com/makeusabrew/audiotee/blob/main/Sources/Core/AudioRecorder.swift). Everything's wired together in [`CLI/AudioTee`](https://github.com/makeusabrew/audiotee/blob/main/Sources/CLI/AudioTee.swift). The rest is just CLI configuration support, output formatting logic, and some utility functions you could probably live without.
 
@@ -25,7 +16,7 @@ Recording system audio is harder than it should be on macOS, and folks often wre
 
 ## Quick start
 
-The following will start capturing audio output from all running programs and write raw PCM audio data to your terminal:
+The following will start capturing audio output from all running programs and write base64-encoded chunks of it to your terminal every 200ms:
 
 ```bash
 git clone git@github.com:makeusabrew/audiotee.git
@@ -33,17 +24,7 @@ cd audiotee
 swift run
 ```
 
-More usefully, you can redirect `stdout` to a file:
+If you're not playing audio when you run it, you'll just see packets full of `AAAAA...` - the base64 version of a bunch of zeroes.
-
-```bash
-swift run audiotee --sample-rate 16000 > output.pcm
-```
-
-Which you can play back using something like `ffplay`:
-
-```bash
-ffplay -f s16le -ar 16000 output.pcm
-```
 
 ## Build
 
@@ -59,23 +40,20 @@ swift build -c release
 Replace the path below with `.build/<arch>/<target>/audiotee`, e.g. `build/arm64-apple-macosx/release/audiotee` for a release build on Apple Silicon.
 
 ```bash
-# Write raw PCM audio to stdout (logs go to stderr)
+# Auto-detect output format (JSON in terminal, binary when piped)
 ./audiotee
 
-# Redirect audio to a file
+# Always use JSON format (terminal-safe)
-./audiotee > output.pcm
+./audiotee --format json
 
-# Pipe to another program
+# Always use binary format (pipe-optimised)
-./audiotee | your_audio_processing_tool
+./audiotee --format binary
-
-# Redirect logs as well
-./audiotee > captured_audio.pcm 2> audiotee.log
 ```
 
 ### Audio conversion
 
 Note that performing sample rate conversion will also convert the output bit depth to
-16-bit - assuming an original depth of 32-bit this results in a loss of dynamic range in exchange for half the output chunk size. For ASR services, 16-bit is sufficient, but it's a behaviour worth being aware of.
+16-bit - assuming an original depth of 32-bit this results in a loss of dynamic range in exchange for half the output chunk size. For ASR services, 16-bit is sufficient, but in any case it's a behaviour worth being aware of.
 
 ```bash
 # Convert to 16kHz mono (useful for ASR services)
@@ -116,33 +94,147 @@ Note that trying to include or exclude a PID which isn't currently playing audio
 ./audiotee --chunk-duration 0.1
 ```
 
-## Output
+## Output formats
 
-AudioTee writes raw PCM audio data directly to `stdout` in chunks. All logging, metadata, and status information is written to `stderr`, allowing for clean separation of audio data from program output.
+AudioTee supports two output formats optimised for different use cases:
 
-### Audio format
+### JSON format (`--format json` or auto in terminal)
 
-- **Format**: Raw PCM audio data
+JSON messages to stdout, one per line. Audio data is base64-encoded for terminal safety.
-- **Channels**: Mono (1 channel)
-- **Sample rate**: Matches your output device's sample rate by default (configurable)
-- **Bit depth**: 32-bit float by default, or 16-bit when sample rate conversion is performed
-- **Endianness**: Little-endian
-- **Chunk duration**: 200ms by default (configurable)
 
-### Logs and monitoring
+### Binary format (`--format binary` or auto when piped)
 
-All program logs are written to `stderr` and can be captured separately:
+JSON metadata lines followed by raw binary audio data. More efficient for piping to other processes.
 
-```bash
+## Protocol
-# Capture audio and logs separately
-./audiotee > audio.pcm 2> audiotee.log
 
-# View logs in real-time while capturing audio
+### Message types
-./audiotee > audio.pcm 2>&1 | grep "AudioTee"
+
+All messages (except raw binary audio chunks) follow this envelope structure:
+
+```json
+{
+  "timestamp": "2024-03-21T15:30:45.123Z",
+  "message_type": "...",
+  "data": { ... }
+}
 ```
 
+#### 1. Metadata
+
+Sent once at startup to describe the audio format:
+
+```json
+{
+  "timestamp": "2024-03-21T15:30:45.123Z",
+  "message_type": "metadata",
+  "data": {
+    "sample_rate": 48000,
+    "channels_per_frame": 1,
+    "bits_per_channel": 32,
+    "is_float": true,
+    "capture_mode": "audio",
+    "device_name": null,
+    "device_uid": null,
+    "encoding": "pcm_f32le"
+  }
+}
+```
+
+#### 2. Stream start
+
+Indicates audio data will follow:
+
+```json
+{
+  "timestamp": "2024-03-21T15:30:45.123Z",
+  "message_type": "stream_start",
+  "data": null
+}
+```
+
+#### 3. Audio data
+
+**JSON format:**
+
+```json
+{
+  "timestamp": "2024-03-21T15:30:45.123Z",
+  "message_type": "audio",
+  "data": {
+    "timestamp": "2024-03-21T15:30:45.123Z",
+    "duration": 0.2,
+    "peak_amplitude": 0.45,
+    "audio_data": "base64_encoded_raw_audio..."
+  }
+}
+```
+
+**Binary format:**
+
+```json
+{
+  "timestamp": "2024-03-21T15:30:45.123Z",
+  "message_type": "audio",
+  "data": {
+    "timestamp": "2024-03-21T15:30:45.123Z",
+    "duration": 0.2,
+    "peak_amplitude": 0.45,
+    "audio_length": 9600
+  }
+}
+```
+
+_Followed immediately by 9600 bytes of raw binary audio data_
+
+#### 4. Stream stop
+
+Sent when recording stops:
+
+```json
+{
+  "timestamp": "2024-03-21T15:30:45.123Z",
+  "message_type": "stream_stop",
+  "data": null
+}
+```
+
+#### 5. Log messages
+
+Info, error, and debug messages (useful for monitoring):
+
+```json
+{
+  "timestamp": "2024-03-21T15:30:45.123Z",
+  "message_type": "info",
+  "data": {
+    "message": "Starting AudioTee...",
+    "context": { "output_format": "auto" }
+  }
+}
+```
+
+### Consuming output
+
+**JSON format:**
+
+1. Parse each line as JSON using the envelope structure
+2. Use `metadata` message to understand the audio format
+3. For `audio` messages, decode `audio_data` from base64 to get raw PCM data
+4. Do something with each chunk of data
+
+**Binary format:**
+
+1. Parse JSON metadata lines using the envelope structure
+2. Use `metadata` message to understand the audio format
+3. For `audio` messages, read `audio_length` bytes of raw binary data after the JSON line
+4. Do something with each chunk of data
+
+**Note**: binary is actually a mixed mode; JSON during boot, JSON packet header information preceding each binary chunk.
+
 ## Command Line options
 
+- `--format, -f`: Output format (`json`, `binary`, `auto`) [default: `auto`]
 - `--include-processes`: Process IDs to tap (space-separated, empty = all processes)
 - `--exclude-processes`: Process IDs to exclude (space-separated, empty = none)
 - `--mute`: Mute processes being tapped
@@ -151,15 +243,35 @@ All program logs are written to `stderr` and can be captured separately:
 
 ## Permissions
 
-There is no provision in the code to pre-emptively check for the required `NSAudioCaptureUsageDescription` permission,
+AudioTee requires system audio recording permissions to function. You can handle these permissions in two ways:
-so you'll be prompted the first time AudioTee tries to record anything. If you want to check and/or request permissions ahead of time, check out [AudioCap's clever TCC probing approach](https://github.com/insidegui/AudioCap/blob/main/AudioCap/ProcessTap/AudioRecordingPermission.swift). Note that some terminal emulators like
+
-iTerm don't always prompt for these permissions (the macOS builtin terminal definitely does), so you
+### Lazy permissions (default approach)
-might need to grant them ahead of time if audiotee looks like it's running but never records anything.
+
+Simply run `./audiotee` and you'll be prompted for permissions the first time AudioTee tries to record audio from the tap. Note that some terminal emulators (at least `iTerm`) will **not** prompt at all, nor will the process fail: instead, AudioTee will happily run but will record a stream of empty data. The built in macOS terminal **does** prompt for permissions and blocks until granted.
+
+### Explicit permissions management
+
+Use the `--permissions` flag to check or request permissions ahead of time:
+
+```bash
+# Check current permission status
+./audiotee --permissions
+
+# Request permissions with user prompt
+./audiotee --permissions --request
+```
+
+Note that the same caveat as above exists here regarding terminal emulators. If you know why, or how to fix it, please help out.
+
+**Exit codes** indicate permission status, making this approach ideal for scripting:
+- `0`: Permissions granted
+- `1`: Permission status unknown  
+- `2`: Permissions denied
 
 ## References
 
 - [Apple Core Audio Taps Documentation](https://developer.apple.com/documentation/coreaudio/capturing-system-audio-with-core-audio-taps)
-- [AudioCap Implementation](https://github.com/insidegui/AudioCap)
+- [AudioCap Implementation](https://github.com/insidegui/AudioCap) - in particular, their awesome TCC probing approach to check for the audio capture permissions, which AudioTee lifts almost in its entirety. Thank you.
 
 ## License
 

Sources/CLI/ArgumentParser.swift

@@ -189,6 +189,11 @@ class SimpleArgumentParser {
         throw ArgumentParserError.invalidValue(optionName, value)
       }
       return doubleValue as! T
+    } else if type == OutputFormat.self {
+      guard let format = OutputFormat(rawValue: value) else {
+        throw ArgumentParserError.invalidValue(optionName, value)
+      }
+      return format as! T
     }
 
     throw ArgumentParserError.invalidValue(optionName, value)

Sources/CLI/AudioTee.swift

@@ -2,11 +2,14 @@ import CoreAudio
 import Foundation
 
 struct AudioTee {
+  var format: OutputFormat = .auto
   var includeProcesses: [Int32] = []
   var excludeProcesses: [Int32] = []
   var mute: Bool = false
   var sampleRate: Double?
   var chunkDuration: Double = 0.2
+  var permissionsMode: Bool = false
+  var requestPermissions: Bool = false
 
   init() {}
 
@@ -17,15 +20,28 @@ struct AudioTee {
       discussion: """
         AudioTee captures system audio using Core Audio taps and streams it as structured output.
 
+        Permission modes:
+        • --permissions: Check current audio recording permissions
+        • --permissions --request: Request audio recording permissions
+
+        Output formats:
+        • json: Base64-encoded audio in JSON messages (safe for terminals)
+        • binary: Raw binary audio with JSON metadata headers (efficient for pipes)
+        • auto: Automatically choose based on whether stdout is a terminal (default)
+
         Process filtering:
         • include-processes: Only tap specified process IDs (empty = all processes)
         • exclude-processes: Tap all processes except specified ones
         • mute: How to handle processes being tapped
 
         Examples:
+          audiotee --permissions                # Check audio recording permissions
+          audiotee --permissions --request      # Request audio recording permissions
           audiotee                              # Auto format, tap all processes
-          audiotee --sample-rate 16000          # Convert to 16kHz mono for ASR
+          audiotee --format=json                # Always use JSON format
-          audiotee --sample-rate 8000           # Convert to 8kHz for telephony
+          audiotee --format=binary              # Always use binary format
+          audiotee --sample-rate=16000          # Convert to 16kHz mono for ASR
+          audiotee --sample-rate=8000           # Convert to 8kHz for telephony
           audiotee --include-processes 1234     # Only tap process 1234
           audiotee --include-processes 1234 5678 9012  # Tap only these processes
           audiotee --exclude-processes 1234 5678       # Tap everything except these
@@ -34,6 +50,9 @@ struct AudioTee {
     )
 
     // Configure arguments
+    parser.addFlag(name: "permissions", help: "Check audio recording permissions")
+    parser.addFlag(name: "request", help: "Request permissions (use with --permissions)")
+    parser.addOption(name: "format", shortName: "f", help: "Output format", defaultValue: "auto")
     parser.addArrayOption(
       name: "include-processes",
       help: "Process IDs to include (space-separated, empty = all processes)")
@@ -53,6 +72,9 @@ struct AudioTee {
       var audioTee = AudioTee()
 
       // Extract values
+      audioTee.permissionsMode = parser.getFlag("permissions")
+      audioTee.requestPermissions = parser.getFlag("request")
+      audioTee.format = try parser.getValue("format", as: OutputFormat.self)
       audioTee.includeProcesses = try parser.getArrayValue("include-processes", as: Int32.self)
       audioTee.excludeProcesses = try parser.getArrayValue("exclude-processes", as: Int32.self)
       audioTee.mute = parser.getFlag("mute")
@@ -86,12 +108,25 @@ struct AudioTee {
       throw ArgumentParserError.validationFailed(
         "Cannot specify both --include-processes and --exclude-processes")
     }
+
+    if requestPermissions && !permissionsMode {
+      throw ArgumentParserError.validationFailed(
+        "--request can only be used with --permissions")
+    }
   }
 
   func run() throws {
+    // Handle permissions mode
+    if permissionsMode {
+      let permissionsHandler = PermissionsHandler(shouldRequest: requestPermissions)
+      permissionsHandler.handle()  // This will exit with appropriate code
+    }
+
+    // Continue with normal audio tapping functionality
     setupSignalHandlers()
 
     Logger.info("Starting AudioTee...")
+    Logger.debug("Using output format: \(format)")
 
     // Validate chunk duration
     guard chunkDuration > 0 && chunkDuration <= 5.0 else {
@@ -132,7 +167,7 @@ struct AudioTee {
       throw ExitCode.failure
     }
 
-    let outputHandler = BinaryAudioOutputHandler()
+    let outputHandler = createOutputHandler(for: format)
     let recorder = AudioRecorder(
       deviceID: deviceID, outputHandler: outputHandler, convertToSampleRate: sampleRate,
       chunkDuration: chunkDuration)
@@ -161,6 +196,17 @@ struct AudioTee {
     }
   }
 
+  private func createOutputHandler(for format: OutputFormat) -> AudioOutputHandler {
+    switch format {
+    case .json:
+      return JSONAudioOutputHandler()
+    case .binary:
+      return BinaryAudioOutputHandler()
+    case .auto:
+      return AutoAudioOutputHandler()
+    }
+  }
+
   private func convertProcessFlags() -> ([Int32], Bool) {
     if !includeProcesses.isEmpty {
       // Include specific processes only
@@ -178,7 +224,7 @@ struct AudioTee {
 // Helper for stderr output
 var standardError = FileHandle.standardError
 
-extension FileHandle: TextOutputStream {
+extension FileHandle: @retroactive TextOutputStream {
   public func write(_ string: String) {
     let data = Data(string.utf8)
     self.write(data)

Sources/CLI/OutputFormat.swift

@@ -0,0 +1,16 @@
+enum OutputFormat: String, CaseIterable {
+  case json = "json"
+  case binary = "binary"
+  case auto = "auto"
+
+  var description: String {
+    switch self {
+    case .json:
+      return "Base64-encoded JSON (terminal-safe)"
+    case .binary:
+      return "Binary with JSON headers (pipe-optimised)"
+    case .auto:
+      return "Auto-detect based on TTY (default)"
+    }
+  }
+}

Sources/CLI/PermissionsHandler.swift

@@ -0,0 +1,47 @@
+import CoreFoundation
+import Foundation
+
+/// Handles audio recording permissions for the CLI, including checking status and requesting permissions.
+/// Uses exit codes to communicate permission status:
+/// - 0: granted (authorized)
+/// - 1: unknown
+/// - 2: denied
+struct PermissionsHandler {
+  private let shouldRequest: Bool
+
+  init(shouldRequest: Bool) {
+    self.shouldRequest = shouldRequest
+  }
+
+  /// Handles the permissions workflow and exits with appropriate exit code
+  func handle() -> Never {
+    let permissionHandler = AudioRecordingPermission()
+
+    if shouldRequest {
+      print("Requesting audio recording permissions...")
+      permissionHandler.request()
+
+      // Wait for the permission request to complete
+      while permissionHandler.status == .unknown {
+        // Run the main run loop to allow DispatchQueue.main.async to execute
+        let result = CFRunLoopRunInMode(CFRunLoopMode.defaultMode, 0.1, true)
+        if result == CFRunLoopRunResult.stopped || result == CFRunLoopRunResult.finished {
+          break
+        }
+      }
+    }
+
+    // Get final status and exit with appropriate code
+    let status = permissionHandler.status
+    print("Audio recording permission status: \(status.rawValue)")
+
+    switch status {
+    case .authorized:
+      exit(0)  // granted
+    case .unknown:
+      exit(1)  // unknown
+    case .denied:
+      exit(2)  // denied
+    }
+  }
+}

Sources/Core/AudioBuffer.swift

@@ -2,64 +2,17 @@ import CoreAudio
 import Foundation
 
 public class AudioBuffer {
-  private var buffer: [UInt8]
+  private var buffer = Data()
-  private var writeIndex: Int = 0
+  private let targetChunkDuration: Double
-  private var readIndex: Int = 0
+  private let streamFormat: AudioStreamBasicDescription
-  private var availableBytes: Int = 0
-  private let maxBufferSize: Int
-
-  private let bytesPerChunk: Int
-  private let chunkDuration: Double
 
   public init(format: AudioStreamBasicDescription, chunkDuration: Double = 0.2) {
-
+    self.streamFormat = format
-    // Pre-calculate chunk parameters
+    self.targetChunkDuration = chunkDuration
-    let bytesPerFrame = Int(format.mBytesPerFrame)
-    let samplesPerChunk = Int(format.mSampleRate * chunkDuration)
-    self.bytesPerChunk = samplesPerChunk * bytesPerFrame
-    self.chunkDuration = Double(samplesPerChunk) / format.mSampleRate
-
-    // Calculate max buffer size to hold ~10 seconds of audio, way more than the maximum we allow
-    let bytesPerSecond = Int(format.mSampleRate) * bytesPerFrame
-    self.maxBufferSize = bytesPerSecond * 10
-
-    // Pre-allocated ring buffer
-    self.buffer = Array(repeating: 0, count: maxBufferSize)
   }
 
   public func append(_ data: Data) {
-    guard availableBytes + data.count <= maxBufferSize else {
+    buffer.append(data)
-      Logger.error(
-        "Audio buffer overflow",
-        context: [
-          "requested": String(data.count),
-          "available": String(maxBufferSize - availableBytes),
-        ])
-      return
-    }
-
-    data.withUnsafeBytes { bytes in
-      let sourceBytes = bytes.bindMemory(to: UInt8.self)
-      let dataSize = sourceBytes.count
-
-      // Check if we can copy in one block (no wrap-around)
-      if writeIndex + dataSize <= maxBufferSize {
-        // only one write needed
-        buffer.replaceSubrange(writeIndex..<writeIndex + dataSize, with: sourceBytes)
-        writeIndex = (writeIndex + dataSize) % maxBufferSize
-      } else {
-        // two writes needed due to wrap-around
-        let firstChunkSize = maxBufferSize - writeIndex
-        let secondChunkSize = dataSize - firstChunkSize
-
-        buffer.replaceSubrange(writeIndex..<maxBufferSize, with: sourceBytes.prefix(firstChunkSize))
-        buffer.replaceSubrange(0..<secondChunkSize, with: sourceBytes.suffix(secondChunkSize))
-
-        writeIndex = secondChunkSize
-      }
-    }
-
-    availableBytes += data.count
   }
 
   public func processChunks() -> [AudioPacket] {
@@ -72,36 +25,37 @@ public class AudioBuffer {
     return packets
   }
 
-  private func nextChunk() -> AudioPacket? {
+  public func flushRemaining() -> AudioPacket? {
-    // Check if we have enough data for a complete chunk
+    guard !buffer.isEmpty else { return nil }
-    guard availableBytes >= bytesPerChunk else { return nil }
-
-    var chunkData = Data(capacity: bytesPerChunk)
-
-    // Check if we can copy in one block (no wrap-around)
-    if readIndex + bytesPerChunk <= maxBufferSize {
-      // one copy needed
-      chunkData.append(contentsOf: buffer[readIndex..<readIndex + bytesPerChunk])
-      readIndex = (readIndex + bytesPerChunk) % maxBufferSize
-    } else {
-      // two copies needed due to wrap-around
-      let firstChunkSize = maxBufferSize - readIndex
-      let secondChunkSize = bytesPerChunk - firstChunkSize
-
-      chunkData.append(contentsOf: buffer[readIndex..<maxBufferSize])
-      chunkData.append(contentsOf: buffer[0..<secondChunkSize])
-
-      readIndex = secondChunkSize
-    }
-
-    availableBytes -= bytesPerChunk
 
     let packet = AudioPacket(
       timestamp: Date(),
-      duration: chunkDuration,
+      duration: 0.0,  // Unknown duration for final chunk
-      rawAudioData: chunkData
+      peakAmplitude: 0.0,
+      rawAudioData: buffer
     )
 
+    buffer.removeAll()
+    return packet
+  }
+
+  private func nextChunk() -> AudioPacket? {
+    let bytesPerFrame = Int(streamFormat.mBytesPerFrame)
+    let samplesPerChunk = Int(streamFormat.mSampleRate * targetChunkDuration)
+    let bytesPerChunk = samplesPerChunk * bytesPerFrame
+
+    guard buffer.count >= bytesPerChunk else { return nil }
+
+    let chunkData = buffer.prefix(bytesPerChunk)
+
+    let packet = AudioPacket(
+      timestamp: Date(),
+      duration: Double(samplesPerChunk) / streamFormat.mSampleRate,
+      peakAmplitude: 0.0,  // No analysis in raw mode
+      rawAudioData: Data(chunkData)
+    )
+
+    buffer.removeFirst(bytesPerChunk)
     return packet
   }
 }

Sources/Core/AudioFormatConverter.swift

@@ -119,6 +119,7 @@ public class AudioFormatConverter {
     return AudioPacket(
       timestamp: packet.timestamp,
       duration: packet.duration,
+      peakAmplitude: packet.peakAmplitude,
       rawAudioData: outputData
     )
   }

Sources/Core/AudioPacket.swift

@@ -3,15 +3,18 @@ import Foundation
 public struct AudioPacket {
   public let timestamp: Date
   public let duration: Double
+  public let peakAmplitude: Float  // useful for level monitoring
   public let rawAudioData: Data
 
   public init(
     timestamp: Date,
     duration: Double,
+    peakAmplitude: Float,
     rawAudioData: Data
   ) {
     self.timestamp = timestamp
     self.duration = duration
+    self.peakAmplitude = peakAmplitude
     self.rawAudioData = rawAudioData
   }
 }

Sources/Core/AudioRecorder.swift

@@ -74,8 +74,7 @@ public class AudioRecorder {
     Logger.info("Audio device started successfully")
   }
 
-  // Note to self, what about installTap? Would require audio engine and a node?
+  // FIXME: note to self, what about installTap? Would require audio engine and a node?
-  // No; AudioEngine.installTap() can only fire as often as 100ms. too slow for us
   private func setupAndStartIOProc() {
     Logger.debug("Creating IO proc")
     var status = AudioDeviceCreateIOProcID(
@@ -127,8 +126,8 @@ public class AudioRecorder {
 
   func stopRecording() {
     // Send any remaining buffered audio, applying conversion if needed
-    audioBuffer?.processChunks().forEach { packet in
+    if let finalPacket = audioBuffer?.flushRemaining() {
-      let processedPacket = converter?.transform(packet) ?? packet
+      let processedPacket = converter?.transform(finalPacket) ?? finalPacket
       outputHandler.handleAudioPacket(processedPacket)
     }
 

Sources/Output/Handlers/AutoOutputHandler.swift

@@ -0,0 +1,31 @@
+import Foundation
+
+/// Auto-detecting output handler based on TTY
+public class AutoAudioOutputHandler: AudioOutputHandler {
+  private let handler: AudioOutputHandler
+
+  public init() {
+    // Auto-detect based on whether stdout is a terminal
+    if isatty(STDOUT_FILENO) != 0 {
+      handler = JSONAudioOutputHandler()
+    } else {
+      handler = BinaryAudioOutputHandler()
+    }
+  }
+
+  public func handleAudioPacket(_ packet: AudioPacket) {
+    handler.handleAudioPacket(packet)
+  }
+
+  public func handleMetadata(_ metadata: AudioStreamMetadata) {
+    handler.handleMetadata(metadata)
+  }
+
+  public func handleStreamStart() {
+    handler.handleStreamStart()
+  }
+
+  public func handleStreamStop() {
+    handler.handleStreamStop()
+  }
+}

Sources/Output/Handlers/BinaryOutputHandler.swift

@@ -5,6 +5,12 @@ public class BinaryAudioOutputHandler: AudioOutputHandler {
   public init() {}
 
   public func handleAudioPacket(_ packet: AudioPacket) {
+    // Create metadata without the audio data
+    let metadata = BinaryPacketHeader(from: packet)
+
+    // Write JSON metadata line
+    Logger.writeMessage(.audio, data: metadata)
+
     // Write raw binary audio data directly to stdout
     FileHandle.standardOutput.write(packet.rawAudioData)
   }

Sources/Output/Handlers/JSONOutputHandler.swift

@@ -0,0 +1,23 @@
+import Foundation
+
+/// Base64-encoded JSON output (terminal-safe)
+public class JSONAudioOutputHandler: AudioOutputHandler {
+  public init() {}
+
+  public func handleAudioPacket(_ packet: AudioPacket) {
+    let jsonPacket = JSONAudioPacket(from: packet)
+    Logger.writeMessage(.audio, data: jsonPacket)
+  }
+
+  public func handleMetadata(_ metadata: AudioStreamMetadata) {
+    Logger.writeMessage(.metadata, data: metadata)
+  }
+
+  public func handleStreamStart() {
+    Logger.writeMessage(.streamStart, data: Optional<String>.none)
+  }
+
+  public func handleStreamStop() {
+    Logger.writeMessage(.streamStop, data: Optional<String>.none)
+  }
+}

Sources/Output/OutputPacketTypes.swift

@@ -0,0 +1,45 @@
+import Foundation
+
+/// JSON-serializable version of AudioPacket with base64-encoded audio data
+public struct JSONAudioPacket: Codable {
+  public let timestamp: Date
+  public let duration: Double
+  public let peakAmplitude: Float
+  public let audioData: String  // base64 encoded audio data
+
+  public enum CodingKeys: String, CodingKey {
+    case timestamp
+    case duration
+    case peakAmplitude = "peak_amplitude"
+    case audioData = "audio_data"
+  }
+
+  public init(from packet: AudioPacket) {
+    self.timestamp = packet.timestamp
+    self.duration = packet.duration
+    self.peakAmplitude = packet.peakAmplitude
+    self.audioData = packet.rawAudioData.base64EncodedString()
+  }
+}
+
+/// Metadata-only packet for binary output (without base64 audio data)
+public struct BinaryPacketHeader: Codable {
+  public let timestamp: Date
+  public let duration: Double
+  public let peakAmplitude: Float
+  public let audioLength: Int  // Length of raw audio data in bytes
+
+  public enum CodingKeys: String, CodingKey {
+    case timestamp
+    case duration
+    case peakAmplitude = "peak_amplitude"
+    case audioLength = "audio_length"
+  }
+
+  public init(from packet: AudioPacket) {
+    self.timestamp = packet.timestamp
+    self.duration = packet.duration
+    self.peakAmplitude = packet.peakAmplitude
+    self.audioLength = packet.rawAudioData.count
+  }
+}

Sources/Permissions/AudioRecordingPermission.swift

@@ -0,0 +1,149 @@
+import OSLog
+import Observation
+import SwiftUI
+
+// Adapted with a huge debt of gratitude from https://github.com/insidegui/AudioCap/blob/main/AudioCap/ProcessTap/AudioRecordingPermission.swift
+
+/// Uses TCC SPI in order to check/request system audio recording permission.
+@Observable
+final class AudioRecordingPermission {
+  // private let logger = Logger(subsystem: kAppSubsystem, category: String(describing: AudioRecordingPermission.self))
+
+  enum Status: String {
+    case unknown
+    case denied
+    case authorized
+  }
+
+  private(set) var status: Status = .unknown
+
+  init() {
+    #if ENABLE_TCC_SPI
+      NotificationCenter.default.addObserver(
+        forName: NSApplication.didBecomeActiveNotification, object: nil, queue: .main
+      ) { [weak self] _ in
+        guard let self else { return }
+        self.updateStatus()
+      }
+
+      updateStatus()
+    #else
+      status = .authorized
+    #endif  // ENABLE_TCC_SPI
+  }
+
+  func request() {
+    #if ENABLE_TCC_SPI
+      // logger.debug(#function)
+      print("DEBUG: TCC SPI request called")
+
+      guard let request = Self.requestSPI else {
+        // logger.fault("Request SPI missing")
+        print("DEBUG: Request SPI is nil - TCC framework loading failed")
+        return
+      }
+
+      print("DEBUG: Calling TCC request function...")
+      request("kTCCServiceAudioCapture" as CFString, nil) { [weak self] granted in
+        guard let self else { return }
+
+        // self.logger.info("Request finished with result: \(granted, privacy: .public)")
+        print("DEBUG: TCC request completed with result: \(granted)")
+
+        DispatchQueue.main.async {
+          print("DEBUG: Updating status on main queue...")
+          if granted {
+            self.status = .authorized
+            print("DEBUG: Status set to authorized")
+          } else {
+            self.status = .denied
+            print("DEBUG: Status set to denied")
+          }
+        }
+      }
+    #else
+      print("DEBUG: ENABLE_TCC_SPI not defined")
+    #endif  // ENABLE_TCC_SPI
+  }
+
+  private func updateStatus() {
+    #if ENABLE_TCC_SPI
+      // logger.debug(#function)
+
+      guard let preflight = Self.preflightSPI else {
+        // logger.fault("Preflight SPI missing")
+        return
+      }
+
+      let result = preflight("kTCCServiceAudioCapture" as CFString, nil)
+
+      if result == 1 {
+        status = .denied
+      } else if result == 0 {
+        status = .authorized
+      } else {
+        status = .unknown
+      }
+    #endif  // ENABLE_TCC_SPI
+  }
+
+  #if ENABLE_TCC_SPI
+    private typealias PreflightFuncType = @convention(c) (CFString, CFDictionary?) -> Int
+    private typealias RequestFuncType = @convention(c) (
+      CFString, CFDictionary?, @escaping (Bool) -> Void
+    ) -> Void
+
+    /// `dlopen` handle to the TCC framework.
+    private static let apiHandle: UnsafeMutableRawPointer? = {
+      let tccPath = "/System/Library/PrivateFrameworks/TCC.framework/Versions/A/TCC"
+      print("DEBUG: Attempting to load TCC framework from: \(tccPath)")
+
+      guard let handle = dlopen(tccPath, RTLD_NOW) else {
+        print("DEBUG: dlopen failed for TCC framework")
+        assertionFailure("dlopen failed")
+        return nil
+      }
+
+      print("DEBUG: TCC framework loaded successfully")
+      return handle
+    }()
+
+    /// `dlsym` function handle for `TCCAccessPreflight`.
+    private static let preflightSPI: PreflightFuncType? = {
+      guard let apiHandle else { return nil }
+
+      let fnName = "TCCAccessPreflight"
+
+      guard let funcSym = dlsym(apiHandle, fnName) else {
+        assertionFailure("Couldn't find symbol")
+        return nil
+      }
+
+      let fn = unsafeBitCast(funcSym, to: PreflightFuncType.self)
+
+      return fn
+    }()
+
+    /// `dlsym` function handle for `TCCAccessRequest`.
+    private static let requestSPI: RequestFuncType? = {
+      guard let apiHandle else {
+        print("DEBUG: No API handle for TCCAccessRequest")
+        return nil
+      }
+
+      let fnName = "TCCAccessRequest"
+      print("DEBUG: Looking for symbol: \(fnName)")
+
+      guard let funcSym = dlsym(apiHandle, fnName) else {
+        print("DEBUG: Couldn't find symbol: \(fnName)")
+        assertionFailure("Couldn't find symbol")
+        return nil
+      }
+
+      print("DEBUG: Found TCCAccessRequest symbol successfully")
+      let fn = unsafeBitCast(funcSym, to: RequestFuncType.self)
+
+      return fn
+    }()
+  #endif  // ENABLE_TCC_SPI
+}

Sources/Utils/Logger.swift

@@ -24,8 +24,8 @@ public class Logger {
     let message = Message(type: type, data: data)
     do {
       let jsonData = try jsonEncoder.encode(message)
-      FileHandle.standardError.write(jsonData)
+      FileHandle.standardOutput.write(jsonData)
-      FileHandle.standardError.write("\n".data(using: .utf8)!)
+      FileHandle.standardOutput.write("\n".data(using: .utf8)!)
     } catch {
       // TODO: handle at some point
     }