Merge branch 'feature/max-channes-count'

Author: shogo4405

Sources/IO/IOAudioMixerSettings.swift

@@ -30,6 +30,10 @@ public struct IOAudioMixerSettings {
     /// Specifies the track settings.
     public var tracks: [UInt8: IOAudioMixerTrackSettings] = .init()
 
+    /// Specifies the maximum number of channels supported by the system
+    /// - Description: The maximum number of channels to be used when the number of channels is 0 (not set). More than 2 channels are not supported by the service. It is defined to prevent audio issues since recording does not support more than 2 channels.
+    public var maximumNumberOfChannels: UInt32 = 2
+
     /// Creates a new instance of a settings.
     public init(
         sampleRate: Float64 = 0,
@@ -49,7 +53,7 @@ public struct IOAudioMixerSettings {
             return nil
         }
         let sampleRate = min(sampleRate == 0 ? format.sampleRate : sampleRate, Self.maximumSampleRate)
-        let channelCount = channels == 0 ? format.channelCount : channels
+        let channelCount = channels == 0 ? min(format.channelCount, maximumNumberOfChannels) : channels
         if let channelLayout = AVAudioUtil.makeChannelLayout(channelCount) {
             return .init(
                 commonFormat: Self.commonFormat,

Tests/IO/IOAudioMixerBySingleTrackTests.swift

@@ -47,19 +47,41 @@ final class IOAudioMixerBySingleTrackTests: XCTestCase {
         XCTAssertEqual(mixer.outputFormat?.sampleRate, 48000)
     }
 
+    func test44100to48000_4ch_2ch() {
+        let result = Result()
+        let mixer = IOAudioMixerBySingleTrack()
+        mixer.delegate = result
+        mixer.settings = .init(
+            sampleRate: 44100, channels: 0
+        )
+        mixer.append(0, buffer: CMAudioSampleBufferFactory.makeSinWave(48000, numSamples: 1024, channels: 4)!)
+        XCTAssertEqual(mixer.outputFormat?.channelCount, 2)
+        XCTAssertEqual(mixer.outputFormat?.sampleRate, 44100)
+        mixer.settings = .init(
+            sampleRate: 48000, channels: 0
+        )
+        mixer.append(0, buffer: CMAudioSampleBufferFactory.makeSinWave(44100, numSamples: 1024, channels: 4)!)
+        mixer.append(0, buffer: CMAudioSampleBufferFactory.makeSinWave(44100, numSamples: 1024, channels: 4)!)
+        XCTAssertEqual(mixer.outputFormat?.channelCount, 2)
+        XCTAssertEqual(mixer.outputFormat?.sampleRate, 48000)
+        XCTAssertEqual(result.outputs.count, 2)
+    }
+
     func test44100to48000_4ch() {
         let result = Result()
         let mixer = IOAudioMixerBySingleTrack()
         mixer.delegate = result
         mixer.settings = .init(
             sampleRate: 44100, channels: 0
         )
+        mixer.settings.maximumNumberOfChannels = 4
         mixer.append(0, buffer: CMAudioSampleBufferFactory.makeSinWave(48000, numSamples: 1024, channels: 4)!)
         XCTAssertEqual(mixer.outputFormat?.channelCount, 4)
         XCTAssertEqual(mixer.outputFormat?.sampleRate, 44100)
         mixer.settings = .init(
             sampleRate: 48000, channels: 0
         )
+        mixer.settings.maximumNumberOfChannels = 4
         mixer.append(0, buffer: CMAudioSampleBufferFactory.makeSinWave(44100, numSamples: 1024, channels: 4)!)
         mixer.append(0, buffer: CMAudioSampleBufferFactory.makeSinWave(44100, numSamples: 1024, channels: 4)!)
         XCTAssertEqual(mixer.outputFormat?.channelCount, 4)