YouTube の音量正規化が Firefox / PipeWire のアプリ音量を 73% に戻すように見えた話

OS: NixOS 26.05
WM: Hyprland
Audio: PipeWire + WirePlumber
Browser: Firefox

- YouTube のシークバー操作
- YouTube の音量バー操作
- 動画遷移

pactl list sink-inputs | rg -n 'Sink Input|application.name|media.name|Volume'

Sink Input #231
  Volume: front-left: 65536 / 100% / 0.00 dB, front-right: 65536 / 100% / 0.00 dB
  application.name = "Firefox"
  media.name = "存在 (@FlawInAffection) / X"
 
Sink Input #377
  Volume: front-left: 48045 / 73% / -8.09 dB, front-right: 48045 / 73% / -8.09 dB
  application.name = "Firefox"
  media.name = "Kep1er 케플러 | 'Yum' M/V - YouTube"

programs.firefox = {
  enable = true;
  package = pkgs.unstable.firefox;
 
  profiles.default = {
    settings = {
      "gfx.webrender.all" = true;
      "layers.acceleration.force-enabled" = true;
      "media.ffmpeg.vaapi.enabled" = true;
      "media.hardware-video-decoding.force-enabled" = true;
      "widget.dmabuf.force-enabled" = true;
    };
  };
};

rg -n \
  'media\.default_volume|media\.volume_scale|volume|youtube|enhancer|sponsor|return-youtube|tampermonkey|violentmonkey|greasemonkey|userscript|extensions\.packages|extensions\.settings' \
  ~/.nixfiles

(bind "XF86AudioRaiseVolume" (luaExec "pactl set-sink-volume @DEFAULT_SINK@ +5%"))
(bind "XF86AudioLowerVolume" (luaExec "pactl set-sink-volume @DEFAULT_SINK@ -5%"))

wpctl settings node.stream.restore-props
rg -n 'Firefox|firefox|YouTube|youtube|volume|mute' ~/.local/state/wireplumber -C 3

Output/Audio:application.name:Firefox={
  "channelMap":["FL", "FR"],
  "mute":false,
  "channelVolumes":[1.000000, 1.000000],
  "volume":1.000000
}

alsa_card.pci-0000_00_1f.3:input:analog-input-mic={
  "channelVolumes":[0.393467, 0.393467]
}

[...document.querySelectorAll("video")].map(v => ({
  volume: v.volume,
  muted: v.muted,
  paused: v.paused,
  currentSrc: v.currentSrc
}))

[
  {
    volume: 0.3940034276447456,
    muted: false,
    paused: false,
    currentSrc: "blob:https://www.youtube.com/..."
  },
  {
    volume: 0.38150479427943834,
    muted: true,
    paused: true
  }
]

(() => {
  const p = document.querySelector("#movie_player");
  const v = [...document.querySelectorAll("video")].find(v => !v.paused)
    ?? document.querySelector("video");
 
  return {
    youtubeUiVolume: p?.getVolume?.(),
    htmlVideoVolume: v?.volume,
    expectedPavucontrol: v ? Math.round(Math.cbrt(v.volume) * 100) + "%" : null,
  };
})();

{
  youtubeUiVolume: 100,
  htmlVideoVolume: 0.3940034276447456,
  expectedPavucontrol: "73%"
}

Volume / Normalized  100% / 39% (content loudness 4.0dB)

YouTube の音量バー: 100%
YouTube の正規化後音量: 39%
HTMLMediaElement.volume: 約 0.39
PipeWire / PulseAudio 上の Firefox stream: 約 73%

desc = Object.getOwnPropertyDescriptor(HTMLMediaElement.prototype, "volume");
setter = desc.set;
 
Object.defineProperty(videoElem, "volume", {
  get: function () {
    return 42;
  },
  set: function (_ignore) {
    var toCall = function () {
      setVolume(volumePanel, videoElem, setter);
    };
    window.setTimeout(toCall, 5);
  }
});

- YouTube の音量バー操作後に Firefox stream が 73% に戻る
- シーク後に pavucontrol の Firefox 音量が下がる
- video.volume が 0.39 前後へ戻る

pactl list sink-inputs |
  awk '
    /^Sink Input #/ { id = substr($3, 2) }
    /application.name = "Firefox"/ { print id }
  ' |
  while read -r id; do
    pactl set-sink-input-volume "$id" 100%
  done

YouTube player
  ↓
HTMLMediaElement.volume = 0.39
  ↓
Firefox
  ↓
PipeWire / PulseAudio sink input = 73%

pactl list sink-inputs | rg -n 'Sink Input|application.name|media.name|Volume|module-stream-restore.id'

wpctl settings node.stream.restore-props

rg -n 'Firefox|firefox|YouTube|youtube|volume|mute' ~/.local/state/wireplumber -C 3

rg -n \
  'media\.default_volume|media\.volume_scale|volume|youtube|enhancer|sponsor|return-youtube|tampermonkey|violentmonkey|greasemonkey|userscript|extensions\.packages|extensions\.settings' \
  ~/.nixfiles

[...document.querySelectorAll("video")].map(v => ({
  volume: v.volume,
  muted: v.muted,
  paused: v.paused,
  currentSrc: v.currentSrc
}))

(() => {
  const p = document.querySelector("#movie_player");
  const v = [...document.querySelectorAll("video")].find(v => !v.paused)
    ?? document.querySelector("video");
 
  return {
    youtubeUiVolume: p?.getVolume?.(),
    htmlVideoVolume: v?.volume,
    expectedPavucontrol: v ? Math.round(Math.cbrt(v.volume) * 100) + "%" : null,
    muted: v?.muted,
    paused: v?.paused,
  };
})();

NixOS / nixfiles:
  原因ではなかった
 
PipeWire / WirePlumber:
  状態を見せていただけで、主因ではなかった
 
Firefox:
  YouTube の media element volume を sink input volume として露出していた
 
YouTube:
  loudness normalization によって実効音量を下げていた
 
解決:
  No YouTube Volume Normalization.user.js