youtube-music/plugins/exponential-volume/front.ts

// "YouTube Music fix volume ratio 0.4" by Marco Pfeiffer
// https://greasyfork.org/en/scripts/397686-youtube-music-fix-volume-ratio/

const exponentialVolume = () => {
  // Manipulation exponent, higher value = lower volume
  // 3 is the value used by pulseaudio, which Barteks2x figured out this gist here: https://gist.github.com/Barteks2x/a4e189a36a10c159bb1644ffca21c02a
  // 0.05 (or 5%) is the lowest you can select in the UI which with an exponent of 3 becomes 0.000125 or 0.0125%
  const EXPONENT = 3;

  const storedOriginalVolumes = new WeakMap<HTMLMediaElement, number>();
  const propertyDescriptor = Object.getOwnPropertyDescriptor(
    HTMLMediaElement.prototype,
    'volume',
  );
  Object.defineProperty(HTMLMediaElement.prototype, 'volume', {
    get(this: HTMLMediaElement) {
      const lowVolume = propertyDescriptor?.get?.call(this) as number ?? 0;
      const calculatedOriginalVolume = lowVolume ** (1 / EXPONENT);

      // The calculated value has some accuracy issues which can lead to problems for implementations that expect exact values.
      // To avoid this, I'll store the unmodified volume to return it when read here.
      // This mostly solves the issue, but the initial read has no stored value and the volume can also change though external influences.
      // To avoid ill effects, I check if the stored volume is somewhere in the same range as the calculated volume.
      const storedOriginalVolume = storedOriginalVolumes.get(this) ?? 0;
      const storedDeviation = Math.abs(
        storedOriginalVolume - calculatedOriginalVolume,
      );

      return storedDeviation < 0.01
        ? storedOriginalVolume
        : calculatedOriginalVolume;
    },
    set(originalVolume: number) {
      const lowVolume = originalVolume ** EXPONENT;
      storedOriginalVolumes.set(this, originalVolume);
      propertyDescriptor?.set?.call(this, lowVolume);
    },
  });
};

export default () =>
  document.addEventListener('apiLoaded', exponentialVolume, {
    once: true,
    passive: true,
  });