backyard/sound/YouTube audio compressor.user.js

// ==UserScript==
// @name         YouTube audio compressor
// @namespace    https://eaguru.guru/
// @version      0.4.2
// @description  Adds an audio compressor option to YouTube videos. Now with over-engineering!
// @author       Vivelin, notwa
// @match        https://*.youtube.com/*
// @updateURL    https://gist.github.com/notwa/9b8466b0c2ca48d756afcd02a5e43739/raw/YouTube%2520audio%2520compressor.user.js
// @run-at       document-idle
// @grant        none
// ==/UserScript==

(function () {
  'use strict';

  let active = false;
  let audioContext = null;
  let source = null;
  let compressor = null;
  let gainIn = null;
  let filterIn = null;
  let filterOut = null;
  let gainOut = null;
  let compressorMenuItem = null;

  // these filters very roughly approximate the inverse of ISO 226:2003 at 70 phons.
  // NOTE: these MUST have all zeros (and poles) within the unit circle,
  //       else the output signal will grow indefinitely (i.e. blow up).
  //       normally, the zeros of an IIR are not subject to this constraint.
  //       however, as a quick 'n' dirty method to reverse the effect
  //       of the filters after compression, i am using their inverses,
  //       with their numerators and denominators swapped.
  //
  // zeroth-degree terms are fixed at 1.0.
  //                1.0 + num_1 * z^-1 + num_2 * z^-2
  // H(z) = gain * -----------------------------------
  //                1.0 + den_1 * z^-1 + den_2 * z^-2
  //                 gain        num_1       num_2       den_1       den_2
  const iir44100 = [+0.4707103, -1.1384015, +0.1384129, -1.5989047, +0.6369472];
  const iir48000 = [+0.4560796, -1.1713186, +0.1713303, -1.6291792, +0.6617519];
  const iir88200 = [+0.3747475, -1.4029588, +0.4029728, -1.7895837, +0.8000784];
  const iir96000 = [+0.3665513, -1.4342713, +0.4342856, -1.8057964, +0.8147329];

  let fancy = true;
  const iirs = {
    44100: iir44100,
    48000: iir48000,
    88200: iir88200,
    96000: iir96000
  }

  function createFilter(coeffs, flip, moreGain = 1.0) {
    const gain = flip ? moreGain / coeffs[0] : moreGain * coeffs[0];
    const b0 = gain;
    const b1 = gain * coeffs[flip ? 3 : 1];
    const b2 = gain * coeffs[flip ? 4 : 2];
    const a0 = 1.0;
    const a1 = coeffs[flip ? 1 : 3];
    const a2 = coeffs[flip ? 2 : 4];
    const num = [b0, b1, b2];
    const den = [a0, a1, a2];
    const filter = audioContext.createIIRFilter(num, den);
    return filter;
  }

  function createCompressorMenuItem() {
    const menuItem = document.createElement('div');
    menuItem.className = 'ytp-menuitem';
    menuItem.setAttribute('role', 'menuitemcheckbox');
    menuItem.setAttribute('aria-checked', 'false');
    menuItem.tabIndex = 0;

    const icon = document.createElement('div');
    icon.className = 'ytp-menuitem-icon';
    menuItem.appendChild(icon);

    const label = document.createElement('div');
    label.className = 'ytp-menuitem-label';
    label.textContent = 'Compressor';
    menuItem.appendChild(label);

    const content = document.createElement('div');
    content.className = 'ytp-menuitem-content';
    const toggleCheckbox = document.createElement('div');
    toggleCheckbox.className = 'ytp-menuitem-toggle-checkbox';
    content.appendChild(toggleCheckbox);
    menuItem.appendChild(content);
    console.log(menuItem);
    return menuItem;
  }

  function setupCompressor(player, ytpPanelMenu) {
    if (!audioContext) {
      audioContext = new AudioContext();
    }
    const iir = iirs[audioContext.sampleRate];
    if (typeof iir === "undefined") {
      fancy = false;
    }

    if (!source) {
      source = audioContext.createMediaElementSource(player);
    }
    if (!gainIn) {
      gainIn = audioContext.createGain();
      gainIn.gain.setValueAtTime(0.7, audioContext.currentTime);
    }
    if (!filterIn && fancy) {
      filterIn = createFilter(iir, false, 2.0);
    }
    if (!compressor) {
      compressor = audioContext.createDynamicsCompressor();
      compressor.threshold.setValueAtTime(-50, audioContext.currentTime);
      compressor.knee.setValueAtTime(40, audioContext.currentTime);
      compressor.ratio.setValueAtTime(12, audioContext.currentTime);
      compressor.attack.setValueAtTime(0.01, audioContext.currentTime);
      compressor.release.setValueAtTime(0.33, audioContext.currentTime);
    }
    if (!filterOut && fancy) {
      filterOut = createFilter(iir, true, 0.5);
    }
    if (!gainOut) {
      gainOut = audioContext.createGain();
      gainOut.gain.setValueAtTime(0.7, audioContext.currentTime);
    }

    if (active) {
      source.connect(gainIn);
    } else {
      source.connect(audioContext.destination);
    }

    if (fancy) {
      gainIn.connect(filterIn);
      filterIn.connect(compressor);
      compressor.connect(filterOut);
      filterOut.connect(gainOut);
    } else {
      gainIn.connect(compressor);
      compressor.connect(gainOut);
    }

    if (!compressorMenuItem) {
      compressorMenuItem = createCompressorMenuItem();
      ytpPanelMenu.appendChild(compressorMenuItem);
      compressorMenuItem.onclick = function () {
        const isActive = compressorMenuItem.getAttribute('aria-checked');
        if (isActive === 'false') {
          compressorMenuItem.setAttribute('aria-checked', 'true');
          source.disconnect(audioContext.destination);
          source.connect(gainIn);
          gainOut.connect(audioContext.destination);
          active = true;
        } else {
          compressorMenuItem.setAttribute('aria-checked', 'false');
          source.disconnect(gainIn);
          gainOut.disconnect(audioContext.destination);
          source.connect(audioContext.destination);
          active = false;
        }
      };
    }
  }

  function startSetup() {
    const player = document.querySelector('#ytd-player video');
    const ytpPanelMenu = document.querySelector('#ytd-player .ytp-settings-menu .ytp-panel-menu');
    if (player && ytpPanelMenu) {
      setupCompressor(player, ytpPanelMenu);
      console.info('Compressor option added');
      return true;
    }

    return false;
  }

  function trySetup() {
    console.debug('Polling for player...');
    const intervalId = window.setInterval(function () {
      if (startSetup()) {
        window.clearInterval(intervalId);
      }
    }, 100);

    const cancelId = window.setTimeout(function () {
      window.clearInterval(intervalId);
    }, 10000);
  }

  if (!startSetup()) {
    trySetup();

    window.addEventListener('yt-navigate-finish', function () {
      trySetup();
    });
  }
})();