potential split between CLI and core library

Sources/AudioTeeCore/Output/AudioOutputProtocol.swift

@@ -0,0 +1,9 @@
+import Foundation
+
+/// Protocol for handling audio output in different formats
+public protocol AudioOutputHandler {
+  func handleAudioPacket(_ packet: AudioPacket)
+  func handleMetadata(_ metadata: AudioStreamMetadata)
+  func handleStreamStart()
+  func handleStreamStop()
+}

Sources/AudioTeeCore/Output/BinaryOutputHandler.swift

@@ -0,0 +1,23 @@
+import Foundation
+
+public class BinaryAudioOutputHandler: AudioOutputHandler {
+  public init() {}
+  
+  public func handleAudioPacket(_ packet: AudioPacket) {
+    // TODO: should we use a DispatchQueue instead of writing directly?
+    // Write raw binary audio data directly to stdout
+    FileHandle.standardOutput.write(packet.data)
+  }
+
+  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/AudioTeeCore/Output/MessageType.swift

@@ -0,0 +1,44 @@
+import Foundation
+
+// Unified message types for all AudioTee output
+public enum MessageType: String, Codable {
+  // Stream lifecycle
+  case metadata
+  case streamStart = "stream_start"
+  case streamStop = "stream_stop"
+
+  // Logging
+  case info
+  case error
+  case debug
+}
+
+// Base message envelope that wraps all outputs
+public struct Message<T: Codable>: Codable {
+  public let timestamp: Date
+  public let type: MessageType
+  public let data: T?
+
+  public enum CodingKeys: String, CodingKey {
+    case timestamp
+    case type = "message_type"
+    case data
+  }
+
+  public init(type: MessageType, data: T? = nil) {
+    self.timestamp = Date()
+    self.type = type
+    self.data = data
+  }
+}
+
+// Simple log data for logging messages
+public struct LogData: Codable {
+  public let message: String
+  public let context: [String: String]?
+
+  public init(message: String, context: [String: String]? = nil) {
+    self.message = message
+    self.context = context
+  }
+}