audio.js

const pMap = require('p-map');
const { join, basename, resolve } = require('path');
const execa = require('execa');
const flatMap = require('lodash/flatMap');

const { getFfmpegCommonArgs, getCutFromArgs } = require('./ffmpeg');
const { readFileStreams } = require('./util');

module.exports = ({ ffmpegPath, ffprobePath, enableFfmpegLog, aMixNormalization, verbose, tmpDir }) => {
  async function createMixedAudioClips({ clips, keepSourceAudio }) {
    return pMap(clips, async (clip, i) => {
      const { duration, layers, transition } = clip;

      async function runInner() {
        const clipAudioPath = join(tmpDir, `clip${i}-audio.flac`);

        async function createSilence() {
          if (verbose) console.log('create silence', duration);
          const args = [
            '-f', 'lavfi', '-i', 'anullsrc=channel_layout=stereo:sample_rate=44100',
            '-sample_fmt', 's32',
            '-ar', '48000',
            '-t', duration,
            '-c:a', 'flac',
            '-y',
            clipAudioPath,
          ];
          await execa(ffmpegPath, args);

          return { silent: true, clipAudioPath };
        }

        // Has user enabled keep source audio?
        if (!keepSourceAudio) return createSilence();

        const audioLayers = layers.filter(({ type, start, stop }) => (
          ['audio', 'video'].includes(type)
          // TODO: We don't support audio for start/stop layers
          && !start && stop == null));

        if (audioLayers.length === 0) return createSilence();

        const processedAudioLayersRaw = await pMap(audioLayers, async (audioLayer, j) => {
          const { path, cutFrom, cutTo, speedFactor } = audioLayer;

          const streams = await readFileStreams(ffprobePath, path);
          if (!streams.some((s) => s.codec_type === 'audio')) return undefined;

          const layerAudioPath = join(tmpDir, `clip${i}-layer${j}-audio.flac`);

          try {
            let atempoFilter;
            if (Math.abs(speedFactor - 1) > 0.01) {
              if (verbose) console.log('audio speedFactor', speedFactor);
              const atempo = (1 / speedFactor);
              if (!(atempo >= 0.5 && atempo <= 100)) { // Required range by ffmpeg
                console.warn(`Audio speed ${atempo} is outside accepted range, using silence (clip ${i})`);
                return undefined;
              }
              atempoFilter = `atempo=${atempo}`;
            }

            const cutToArg = (cutTo - cutFrom) * speedFactor;

            const args = [
              ...getFfmpegCommonArgs({ enableFfmpegLog }),
              ...getCutFromArgs({ cutFrom }),
              '-i', path,
              '-t', cutToArg,
              '-sample_fmt', 's32',
              '-ar', '48000',
              '-map', 'a:0', '-c:a', 'flac',
              ...(atempoFilter ? ['-filter:a', atempoFilter] : []),
              '-y',
              layerAudioPath,
            ];

            // console.log(args);
            await execa(ffmpegPath, args);

            return {
              layerAudioPath,
              audioLayer,
            };
          } catch (err) {
            if (verbose) console.error('Cannot extract audio from video', path, err);
            // Fall back to silence
            return undefined;
          }
        }, { concurrency: 4 });

        const processedAudioLayers = processedAudioLayersRaw.filter((p) => p);

        if (processedAudioLayers.length < 1) return createSilence();

        if (processedAudioLayers.length === 1) return { clipAudioPath: processedAudioLayers[0].layerAudioPath };

        // Merge/mix all layers' audio
        const weights = processedAudioLayers.map(({ audioLayer }) => (audioLayer.mixVolume != null ? audioLayer.mixVolume : 1));
        const args = [
          ...getFfmpegCommonArgs({ enableFfmpegLog }),
          ...flatMap(processedAudioLayers, ({ layerAudioPath }) => ['-i', layerAudioPath]),
          '-filter_complex', `amix=inputs=${processedAudioLayers.length}${aMixNormalization ? ':normalize=0' : ''}:duration=longest:weights=${weights.join(' ')}`,
          '-c:a', 'flac',
          '-y',
          clipAudioPath,
        ];

        await execa(ffmpegPath, args);
        return { clipAudioPath };
      }

      const { clipAudioPath, silent } = await runInner();

      return {
        path: resolve(clipAudioPath), // https://superuser.com/a/853262/658247
        transition,
        silent,
      };
    }, { concurrency: 4 });
  }

  async function crossFadeConcatClipAudio(clipAudio) {
    if (clipAudio.length < 2) {
      return clipAudio[0].path;
    }

    const outPath = join(tmpDir, 'audio-concat.flac');

    if (verbose) console.log('Combining audio', clipAudio.map(({ path }) => basename(path)));

    let inStream = '[0:a]';
    const filterGraph = clipAudio.slice(0, -1).map(({ transition }, i) => {
      const outStream = `[concat${i}]`;

      const epsilon = 0.0001; // If duration is 0, ffmpeg seems to default to 1 sec instead, hence epsilon.
      let ret = `${inStream}[${i + 1}:a]acrossfade=d=${Math.max(epsilon, transition.duration)}:c1=${transition.audioOutCurve || 'tri'}:c2=${transition.audioInCurve || 'tri'}`;

      inStream = outStream;

      if (i < clipAudio.length - 2) ret += outStream;
      return ret;
    }).join(',');

    const args = [
      ...getFfmpegCommonArgs({ enableFfmpegLog }),
      ...(flatMap(clipAudio, ({ path }) => ['-i', path])),
      '-filter_complex',
      filterGraph,
      '-c', 'flac',
      '-y',
      outPath,
    ];
    await execa(ffmpegPath, args);

    return outPath;
  }

  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}${aMixNormalization ? ':normalize=0' : ''}:duration=first:dropout_transition=0:weights=${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
    if (clips.length === 0) return undefined;

    // No need to process audio if none of these are satisfied
    if (!(keepSourceAudio || arbitraryAudio.length > 0)) return undefined;

    console.log('Extracting audio/silence from all clips');

    // Mix audio from each clip as separate files (or silent audio of appropriate length for clips with no audio)
    const clipAudio = await createMixedAudioClips({ clips, keepSourceAudio });

    // Return no audio if only silent clips and no arbitrary audio
    if (clipAudio.every((ca) => ca.silent) && arbitraryAudio.length === 0) return undefined;

    // Merge & fade the clip audio files
    const concatedClipAudioPath = await crossFadeConcatClipAudio(clipAudio);

    const streams = [
      // The first stream is required, as it determines the length of the output audio.
      // All other streams will be truncated to its length
      { path: concatedClipAudioPath, mixVolume: clipsAudioVolume },

      ...arbitraryAudio,
    ];

    console.log('Mixing clip audio with arbitrary audio');

    if (streams.length < 2) return concatedClipAudioPath;

    const mixedFile = await mixArbitraryAudio({ streams, audioNorm, outputVolume });
    return mixedFile;
  }

  return {
    editAudio,
  };
};