Function mixArbitraryAudio

audio.js:159–199

({ streams, audioNorm, outputVolume })

  }

  async function mixArbitraryAudio({ streams, audioNorm, outputVolume }) {
    let maxGain = 30;
    let gaussSize = 5;
    if (audioNorm) {
      if (audioNorm.gaussSize != null) gaussSize = audioNorm.gaussSize;
      if (audioNorm.maxGain != null) maxGain = audioNorm.maxGain;
    }
    const enableAudioNorm = audioNorm && audioNorm.enable;

    // https://stackoverflow.com/questions/35509147/ffmpeg-amix-filter-volume-issue-with-inputs-of-different-duration
    let filterComplex = streams.map(({ start, cutFrom, cutTo }, i) => {
      const cutToArg = (cutTo != null ? `:end=${cutTo}` : '');
      const apadArg = i > 0 ? ',apad' : ''; // Don't pad the first track (audio from video clips with correct duration)

      return `[${i}]atrim=start=${cutFrom || 0}${cutToArg},adelay=delays=${Math.floor((start || 0) * 1000)}:all=1${apadArg}[a${i}]`;
    }).join(';');

    const volumeArg = outputVolume != null ? `,volume=${outputVolume}` : '';
    const audioNormArg = enableAudioNorm ? `,dynaudnorm=g=${gaussSize}:maxgain=${maxGain}` : '';
    filterComplex += `;${streams.map((s, i) => `[a${i}]`).join('')}amix=inputs=${streams.length}:duration=first:dropout_transition=0:weights=${streams.map((s) => (s.mixVolume != null ? s.mixVolume : 1)).join(' ')}${audioNormArg}${volumeArg}`;

    const mixedAudioPath = join(tmpDir, 'audio-mixed.flac');

    const args = [
      ...getFfmpegCommonArgs({ enableFfmpegLog }),
      ...(flatMap(streams, ({ path, loop }) => ([
        '-stream_loop', (loop || 0),
        '-i', path,
      ]))),
      '-filter_complex', filterComplex,
      '-c:a', 'flac',
      '-y',
      mixedAudioPath,
    ];

    if (verbose) console.log(args.join(' '));

    await execa(ffmpegPath, args);

    return mixedAudioPath;
  }

  async function editAudio({ keepSourceAudio, clips, arbitraryAudio, clipsAudioVolume, audioNorm, outputVolume }) {
    // We need clips to process audio, because we need to know duration