web-voice-detection/src/common/resampler.ts

A WebAssembly-powered Voice Activity Detection library for the browser.

// TypeScript code
import { log } from "./logging";

type ResamplerOptions = {
  nativeSampleRate: number;
  targetSampleRate: number;
  targetFrameSize: number;
};

export class Resampler {
  inputBuffer: Array<number>;

  constructor(public options: ResamplerOptions) {
    if (options.nativeSampleRate < 16000) {
      log.error(
        "nativeSampleRate is too low. Should have 16000 = targetSampleRate <= nativeSampleRate",
      );
    }
    this.inputBuffer = [];
  }

  process = (audioFrame: Float32Array): Float32Array[] => {
    const outputFrames: Array<Float32Array> = [];
    this.fillInputBuffer(audioFrame);

    while (this.hasEnoughDataForFrame()) {
      const outputFrame = this.generateOutputFrame();
      outputFrames.push(outputFrame);
    }

    return outputFrames;
  };

  *stream(this: Resampler, audioFrame: Float32Array): Generator<Float32Array> {
    this.fillInputBuffer(audioFrame);

    while (this.hasEnoughDataForFrame()) {
      const outputFrame = this.generateOutputFrame();
      yield outputFrame;
    }
  }

  private fillInputBuffer(audioFrame: Float32Array) {
    for (const sample of audioFrame) {
      this.inputBuffer.push(sample);
    }
  }

  private hasEnoughDataForFrame(): boolean {
    return (
      (this.inputBuffer.length * this.options.targetSampleRate) / this.options.nativeSampleRate >=
      this.options.targetFrameSize
    );
  }

  private generateOutputFrame(): Float32Array {
    const outputFrame = new Float32Array(this.options.targetFrameSize);
    let outputIndex = 0;
    let inputIndex = 0;

    while (outputIndex < this.options.targetFrameSize) {
      let sum = 0;
      let num = 0;
      while (
        inputIndex <
        Math.min(
          this.inputBuffer.length,
          ((outputIndex + 1) * this.options.nativeSampleRate) / this.options.targetSampleRate,
        )
      ) {
        const value = this.inputBuffer[inputIndex];
        if (value !== undefined) {
          sum += value;
          num++;
        }
        inputIndex++;
      }
      outputFrame[outputIndex] = sum / num;
      outputIndex++;
    }

    this.inputBuffer = this.inputBuffer.slice(inputIndex);
    return outputFrame;
  }
}