Converting Raw PCM to WAV Format

Gemini TTS returns raw PCM data without a WAV header. Add a proper WAV header for compatibility.

WAV Header Structure

function createWavHeader(dataLength: number, sampleRate: number, channels: number, bitsPerSample: number): Buffer {
  const header = Buffer.alloc(44);

  // RIFF chunk descriptor
  header.write('RIFF', 0);                   // ChunkID
  header.writeUInt32LE(36 + dataLength, 4);  // ChunkSize
  header.write('WAVE', 8);                   // Format

  // fmt sub-chunk
  header.write('fmt ', 12);                  // Subchunk1ID
  header.writeUInt32LE(16, 16);              // Subchunk1Size (16 for PCM)
  header.writeUInt16LE(1, 20);               // AudioFormat (1 = PCM)
  header.writeUInt16LE(channels, 22);        // NumChannels
  header.writeUInt32LE(sampleRate, 24);      // SampleRate
  header.writeUInt32LE(sampleRate * channels * bitsPerSample / 8, 28);  // ByteRate
  header.writeUInt16LE(channels * bitsPerSample / 8, 32);               // BlockAlign
  header.writeUInt16LE(bitsPerSample, 34);   // BitsPerSample

  // data sub-chunk
  header.write('data', 36);                  // Subchunk2ID
  header.writeUInt32LE(dataLength, 40);      // Subchunk2Size

  return header;
}

Complete Conversion

function pcmToWav(pcmBuffer: Buffer, sampleRate: number = 24000, channels: number = 1, bitsPerSample: number = 16): Buffer {
  const header = createWavHeader(pcmBuffer.length, sampleRate, channels, bitsPerSample);
  return Buffer.concat([header, pcmBuffer]);
}

Usage with Gemini TTS

import { createWavHeader } from './audio-utils';

// Gemini returns raw PCM
const pcmBuffer = Buffer.from(audioPart.inlineData.data, 'base64');

// Convert to WAV
const wavBuffer = pcmToWav(pcmBuffer, 24000, 1, 16);

// Save WAV file
fs.writeFileSync('output.wav', wavBuffer);

Constants for Gemini TTS

const AUDIO_CONFIG = {
  SAMPLE_RATE: 24000,    // 24 kHz
  CHANNELS: 1,           // Mono
  BYTES_PER_SAMPLE: 2,   // 16-bit = 2 bytes
};

Header Field Explanations

Byte Order

All multi-byte values use little-endian byte order (UInt32LE, UInt16LE).