resamplePcmTo8k (telephony-audio.ts)

Resamples 16-bit PCM audio to 8kHz telephony sample rate using linear interpolation.

const TELEPHONY_SAMPLE_RATE = 8000;

function clamp16(value: number): number {
  return Math.max(-32768, Math.min(32767, value));
}

/**
 * Resample 16-bit PCM (little-endian mono) to 8kHz using linear interpolation.
 */
export function resamplePcmTo8k(input: Buffer, inputSampleRate: number): Buffer {
  if (inputSampleRate === TELEPHONY_SAMPLE_RATE) {
    return input;
  }
  const inputSamples = Math.floor(input.length / 2);
  if (inputSamples === 0) {
    return Buffer.alloc(0);
  }

  const ratio = inputSampleRate / TELEPHONY_SAMPLE_RATE;
  const outputSamples = Math.floor(inputSamples / ratio);
  const output = Buffer.alloc(outputSamples * 2);

  for (let i = 0; i < outputSamples; i++) {
    const srcPos = i * ratio;
    const srcIndex = Math.floor(srcPos);
    const frac = srcPos - src

... (truncated -- full source via MCP)