feat(AudioStreaming): Add multichannel audio playback groundwork

AudioStreaming/OggVorbis/VorbisFileDecoder.swift

@@ -120,6 +120,11 @@ final class VorbisFileDecoder {
             switch channels {
             case 1: layoutTag = kAudioChannelLayoutTag_Mono
             case 2: layoutTag = kAudioChannelLayoutTag_Stereo
+            // Vorbis uses FL, FC, FR, RL, RR, LFE channel order. The MPEG
+            // 5.1 layout instead expects FL, FR, FC, LFE, RL, RR, so tagging
+            // Vorbis PCM as MPEG 5.1 misidentifies four of the six channels.
+            // Ogg_5_1 describes the channel order emitted by the Vorbis decoder.
+            case 6: layoutTag = kAudioChannelLayoutTag_Ogg_5_1
             default: layoutTag = kAudioChannelLayoutTag_Unknown | UInt32(channels)
             }
 

AudioStreaming/Streaming/AudioPlayer/AudioPlayer.swift

@@ -146,7 +146,15 @@ open class AudioPlayer {
     }
 
     /// An `AVAudioFormat` object for the canonical audio stream
-    private var outputAudioFormat: AVAudioFormat = .init(commonFormat: .pcmFormatFloat32, sampleRate: 44100.0, channels: 2, interleaved: true)!
+    private let outputAudioFormat: AVAudioFormat = {
+        let channelLayout = AVAudioChannelLayout(layoutTag: kAudioChannelLayoutTag_MPEG_5_1_A)!
+        return AVAudioFormat(
+            commonFormat: .pcmFormatFloat32,
+            sampleRate: 44100.0,
+            interleaved: true,
+            channelLayout: channelLayout
+        )
+    }()
 
     /// Keeps track of the player's state before being paused.
     private var stateBeforePaused: InternalState = .initial

AudioStreaming/Streaming/AudioPlayer/AudioRendererContext.swift

@@ -38,7 +38,10 @@ final class AudioRendererContext {
         framesRequiredForDataAfterSeekPlaying = Double(canonicalStream.mSampleRate) * Double(configuration.gracePeriodAfterSeekInSeconds)
 
         let dataByteSize = Int(canonicalStream.mSampleRate * configuration.bufferSizeInSeconds) * Int(canonicalStream.mBytesPerFrame)
-        inOutAudioBufferList = allocateBufferList(dataByteSize: dataByteSize)
+        inOutAudioBufferList = allocateBufferList(
+            dataByteSize: dataByteSize,
+            channelCount: canonicalStream.mChannelsPerFrame
+        )
 
         audioBuffer = inOutAudioBufferList[0].mBuffers
 
@@ -71,14 +74,17 @@ final class AudioRendererContext {
 ///
 /// - parameter dataByteSize: An `Int` value indicating the size that the buffer will hold
 /// - Returns: An `UnsafeMutablePointer<AudioBufferList>` object
-private func allocateBufferList(dataByteSize: Int) -> UnsafeMutablePointer<AudioBufferList> {
+private func allocateBufferList(
+    dataByteSize: Int,
+    channelCount: UInt32
+) -> UnsafeMutablePointer<AudioBufferList> {
     let _bufferList = AudioBufferList.allocate(maximumBuffers: 1)
 
     _bufferList[0].mDataByteSize = UInt32(dataByteSize)
     let alignment = MemoryLayout<UInt8>.alignment
     let mData = UnsafeMutableRawPointer.allocate(byteCount: dataByteSize, alignment: alignment)
     _bufferList[0].mData = mData
-    _bufferList[0].mNumberChannels = 2
+    _bufferList[0].mNumberChannels = channelCount
 
     return _bufferList.unsafeMutablePointer
 }

AudioStreaming/Streaming/AudioPlayer/Processors/AudioFileStreamProcessor.swift

@@ -244,10 +244,47 @@ final class AudioFileStreamProcessor {
                 return
             }
         }
+        configureChannelLayouts(for: audioConverter, inputChannels: inputFormat.mChannelsPerFrame)
         self.inputFormat = inputFormat
         assignMagicCookieToConverterIfNeeded()
     }
 
+    private func configureChannelLayouts(
+        for converter: AudioConverterRef?,
+        inputChannels: UInt32
+    ) {
+        guard let converter else { return }
+
+        if let inputLayoutTag = channelLayoutTag(for: inputChannels),
+           let inputLayout = AVAudioChannelLayout(layoutTag: inputLayoutTag) {
+            AudioConverterSetProperty(
+                converter,
+                kAudioConverterInputChannelLayout,
+                UInt32(MemoryLayout<AudioChannelLayout>.size),
+                inputLayout.layout
+            )
+        }
+
+        guard let outputLayout = AVAudioChannelLayout(
+            layoutTag: kAudioChannelLayoutTag_MPEG_5_1_A
+        ) else { return }
+        AudioConverterSetProperty(
+            converter,
+            kAudioConverterOutputChannelLayout,
+            UInt32(MemoryLayout<AudioChannelLayout>.size),
+            outputLayout.layout
+        )
+    }
+
+    private func channelLayoutTag(for channelCount: UInt32) -> AudioChannelLayoutTag? {
+        return switch channelCount {
+        case 1: kAudioChannelLayoutTag_Mono
+        case 2: kAudioChannelLayoutTag_Stereo
+        case 6: kAudioChannelLayoutTag_MPEG_5_1_A
+        default: nil
+        }
+    }
+
     private func assignMagicCookieToConverterIfNeeded() {
         // magic cookie info
         if let fileStream = audioFileStream {

AudioStreaming/Streaming/AudioPlayer/Processors/AudioPlayerRenderProcessor.swift

@@ -113,7 +113,7 @@ final class AudioPlayerRenderProcessor: NSObject {
         if used > 0 && !waitForBuffer && playingEntry != nil && state.contains(.running) && state != .paused {
             if end > start {
                 let framesToCopy = min(inNumberFrames, used)
-                bufferList.mBuffers.mNumberChannels = 2
+                bufferList.mBuffers.mNumberChannels = outputAudioFormat.mChannelsPerFrame
                 bufferList.mBuffers.mDataByteSize = frameSizeInBytes * framesToCopy
 
                 if isMuted {
@@ -155,7 +155,7 @@ final class AudioPlayerRenderProcessor: NSObject {
                     #endif
                     frameToCopy = 0
                 }
-                bufferList.mBuffers.mNumberChannels = 2
+                bufferList.mBuffers.mNumberChannels = outputAudioFormat.mChannelsPerFrame
                 bufferList.mBuffers.mDataByteSize = frameSizeInBytes * frameToCopy
 
                 if isMuted {
@@ -172,7 +172,7 @@ final class AudioPlayerRenderProcessor: NSObject {
                 let delta = inNumberFrames - frameToCopy
                 if delta > 0 {
                     moreFramesToCopy = min(delta, end)
-                    bufferList.mBuffers.mNumberChannels = 2
+                    bufferList.mBuffers.mNumberChannels = outputAudioFormat.mChannelsPerFrame
                     bufferList.mBuffers.mDataByteSize += frameSizeInBytes * moreFramesToCopy
                     if let ioBufferData = bufferList.mBuffers.mData {
                         if isMuted {

AudioStreaming/Streaming/AudioPlayer/Processors/OggVorbisStreamProcessor.swift

@@ -291,12 +291,21 @@ final class OggVorbisStreamProcessor {
     private func createAudioConverter(from sourceFormat: AVAudioFormat, to destFormat: AudioStreamBasicDescription) {
         audioConverter = nil
 
-        var dest = destFormat
+        let dest = destFormat
 
-        guard let destAVFormat = AVAudioFormat(streamDescription: &dest) else {
-            Logger.error("Failed to create output AVAudioFormat", category: .audioRendering)
+        guard let channelLayout = AVAudioChannelLayout(
+            layoutTag: kAudioChannelLayoutTag_MPEG_5_1_A
+        ) else {
+            Logger.error("Failed to create 5.1 output channel layout", category: .audioRendering)
             return
         }
+
+        let destAVFormat = AVAudioFormat(
+            commonFormat: .pcmFormatFloat32,
+            sampleRate: dest.mSampleRate,
+            interleaved: true,
+            channelLayout: channelLayout
+        )
 
         guard let converter = AVAudioConverter(from: sourceFormat, to: destAVFormat) else {
             Logger.error("Failed to create AVAudioConverter", category: .audioRendering)