feat(multichannel): Combine all audio channels

src/recorder/index.ts

@@ -17,6 +17,22 @@ const SafeAudioContext: typeof AudioContext = (window as any).AudioContext || (w
 const createGain = (ctx: AudioContext) => (ctx.createGain || (ctx as any).createGainNode).call(ctx);
 const createScriptProcessor = (ctx: AudioContext) =>
  (ctx.createScriptProcessor || (ctx as any).createJavaScriptNode).call(ctx, 4096, 1, 1);
+const clamp = (min: number, max: number) => (value: number): number => Math.min(Math.max(value, min), max);
+
+const mergeAudioChannels = (buffer: AudioBuffer): Float32Array => {
+ const channels = new Array(buffer.numberOfChannels).fill(null).map((_, i) => buffer.getChannelData(i));
+ const mergedChannelData: number[] = [];
+
+ for (let index = 0; index < channels[0].length; index++) {
+ const mergedSample = channels.reduce(
+ (result, channel) => clamp(-2_147_483_648, 2_147_483_647)(result + channel[index]),
+ 0
+ );
+ mergedChannelData.push(mergedSample);
+ }
+
+ return new Float32Array(mergedChannelData);
+};
 
 export class Mp3MediaRecorder extends EventTarget {
  stream: MediaStream;
@@ -58,7 +74,7 @@ export class Mp3MediaRecorder extends EventTarget {
  throw this.getStateError('start');
  }
  this.processorNode.onaudioprocess = (event) => {
- this.worker.postMessage(dataAvailableMessage(event.inputBuffer.getChannelData(0)));
+ this.worker.postMessage(dataAvailableMessage(mergeAudioChannels(event.inputBuffer)));
  };
  this.processorNode.connect(this.audioContext.destination);
  if (this.audioContext.state === 'closed') {

src/types/post-message.type.ts

@@ -17,7 +17,7 @@ export const workerRecordingMessage = () => ({
  type: PostMessageType.WORKER_RECORDING as PostMessageType.WORKER_RECORDING,
 });
 
-export const dataAvailableMessage = (data: ArrayLike<number>) => ({
+export const dataAvailableMessage = (data: Float32Array) => ({
  type: PostMessageType.DATA_AVAILABLE as PostMessageType.DATA_AVAILABLE,
  data,
 });