How to Build a Mp4 To Avi Converter

// Browser-based conversion using FFmpeg WASM
  import { FFmpeg } from '@ffmpeg/ffmpeg';
  import { fetchFile } from '@ffmpeg/util';

  async function convertMp4ToAvi(inputFile, options = {}) {
  const { codec = 'copy', quality = 'high' } = options;
  const ffmpeg = new FFmpeg();
  await ffmpeg.load();

  await ffmpeg.writeFile('input.mp4', await fetchFile(inputFile));

  const args = ['-i', 'input.mp4'];

  if (codec === 'copy') {
    // Fast remux: no re-encoding, nearly instant
    args.push('-c:v', 'copy', '-c:a', 'copy');
  } else if (codec === 'mjpeg') {
    // MJPEG for legacy editing software
    const qscale = quality === 'high' ? '2' : quality === 'medium' ? '5' : '10';
    args.push('-c:v', 'mjpeg', '-q:v', qscale, '-c:a', 'pcm_s16le');
  } else {
    // Xvid/MPEG-4 Part 2 for broad AVI compatibility
    const bitrate = quality === 'high' ? '5000k' : quality === 'medium' ? '2500k' : '1000k';
    args.push('-c:v', 'mpeg4', '-b:v', bitrate, '-c:a', 'mp3', '-b:a', '192k');
  }

  args.push('output.avi');
  await ffmpeg.exec(args);

  const data = await ffmpeg.readFile('output.avi');
  return new Blob([data.buffer], { type: 'video/x-msvideo' });
  }