Merge pull request #1280 from stream-labs/bugfix/audio-channel-map

Improve audio channel mapping
shogo4405 · Sep 2, 2023 · bc4615a · bc4615a
2 parents 2aa1489 + 507eed3
commit bc4615a
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Showing 3 changed files with 56 additions and 13 deletions.
diff --git a/Sources/Codec/AudioCodec.swift b/Sources/Codec/AudioCodec.swift
@@ -49,17 +49,17 @@ public class AudioCodec {
     }
 
     /// Creates a channel map for specific input and output format
-    /// - Examples:
-    ///   - Input channel count is 4 and 2, result:  [0, 1, -1, -1]
-    ///   - Input channel count is 2 and 2, result:  [0, 1]
-    static func makeChannelMap(from fromFormat: AVAudioFormat, to toFormat: AVAudioFormat) -> [NSNumber] {
-        let inChannels = Int(fromFormat.channelCount)
-        let outChannels = Int(toFormat.channelCount)
-        let channelIndexes = Array(0...inChannels - 1)
-        return channelIndexes
-            .prefix(outChannels)
-            .map { NSNumber(value: $0) }
-            + Array(repeating: -1, count: max(0, inChannels - outChannels))
+    static func makeChannelMap(inChannels: Int, outChannels: Int, outputChannelsMap: [Int: Int]) -> [NSNumber] {
+        var result = Array(repeating: -1, count: outChannels)
+        for inputIndex in 0..<min(inChannels, outChannels) {
+            result[inputIndex] = inputIndex
+        }
+        for currentIndex in 0..<outChannels {
+            if let inputIndex = outputChannelsMap[currentIndex], inputIndex < inChannels {
+                result[currentIndex] = inputIndex
+            }
+        }
+        return result.map { NSNumber(value: $0) }
     }
 
     /// Specifies the delegate.
@@ -194,7 +194,10 @@ public class AudioCodec {
         logger.debug("inputFormat: \(inputFormat)")
         logger.debug("outputFormat: \(outputFormat)")
         let converter = AVAudioConverter(from: inputFormat, to: outputFormat)
-        converter?.channelMap = Self.makeChannelMap(from: inputFormat, to: outputFormat)
+        let channelMap = Self.makeChannelMap(inChannels: Int(inputFormat.channelCount), outChannels: Int(outputFormat.channelCount),
+                outputChannelsMap: settings.outputChannelsMap)
+        logger.debug("channelMap: \(channelMap)")
+        converter?.channelMap = channelMap
         settings.apply(converter, oldValue: nil)
         if converter == nil {
             delegate?.audioCodec(self, errorOccurred: .failedToCreate(from: inputFormat, to: outputFormat))

diff --git a/Sources/Codec/AudioCodecSettings.swift b/Sources/Codec/AudioCodecSettings.swift
@@ -122,14 +122,23 @@ public struct AudioCodecSettings: Codable {
 
     /// Specifies the output format.
     public var format: AudioCodecSettings.Format
+
+    /// Map of the output to input channels
+    public var outputChannelsMap: [Int: Int]
 
     /// Create an new AudioCodecSettings instance.
     public init(
         bitRate: Int = 64 * 1000,
-        format: AudioCodecSettings.Format = .aac
+        format: AudioCodecSettings.Format = .aac,
+        outputChannelsMap: [Int: Int] = [0: 0, 1: 1]
     ) {
         self.bitRate = bitRate
         self.format = format
+        self.outputChannelsMap = outputChannelsMap
+    }
+
+    func recreateConverter(_ rhs: AudioCodecSettings) -> Bool {
+        !(outputChannelsMap == rhs.outputChannelsMap)
     }
 
     func apply(_ converter: AVAudioConverter?, oldValue: AudioCodecSettings?) {

diff --git a/Tests/Codec/AudioCodecTests.swift b/Tests/Codec/AudioCodecTests.swift
@@ -93,5 +93,36 @@ final class AudioCodecTests: XCTestCase {
             encoder.appendSampleBuffer(sampleBuffer)
         }
     }
+
+    func testChannelMaps() {
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 1, outputChannelsMap: [:]), [0])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 1, outputChannelsMap: [0: 0]), [0])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 1, outputChannelsMap: [0: 0, 1: 1]), [0])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 1, outputChannelsMap: [0: -1]), [-1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 1, outputChannelsMap: [Int.max: Int.max]), [0])
+
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 2, outputChannelsMap: [:]), [0, -1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 2, outputChannelsMap: [0: 0]), [0, -1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 2, outputChannelsMap: [0: 1]), [0, -1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 2, outputChannelsMap: [0: -1, 1: -1]), [-1, -1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 2, outputChannelsMap: [0: 1, 1: Int.max]), [0, 1])
+
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 1, outputChannelsMap: [:]), [0])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 1, outputChannelsMap: [0: 0]), [0])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 1, outputChannelsMap: [0: 1]), [1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 1, outChannels: 1, outputChannelsMap: [0: -1]), [-1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 1, outputChannelsMap: [Int.max: 0]), [0])
+
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 2, outputChannelsMap: [:]), [0, 1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 2, outputChannelsMap: [0: 0]), [0, 1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 2, outputChannelsMap: [0: 0, 1: 1]), [0, 1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 2, outputChannelsMap: [0: -1, 1: -1]), [-1, -1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 2, outputChannelsMap: [0: -1, 1: 1]), [-1, 1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 2, outputChannelsMap: [0: 0, 1: 1, Int.max: Int.max]), [0, 1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 2, outChannels: 2, outputChannelsMap: [0: 0, 1: Int.max]), [0, 1])
+
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 12, outChannels: 2, outputChannelsMap: [:]), [0, 1])
+        XCTAssertEqual(AudioCodec.makeChannelMap(inChannels: 12, outChannels: 2, outputChannelsMap: [0: -1, 1: 11]), [-1, 11])
+    }
 }