Examine source code of Etude · Looper - transpose, slow down, loop

{
  "manifest_version": 3,
  "name": "Etude Looper — transpose & slow down YouTube",
  "version": "0.1.4",
  "description": "Change any YouTube video's key and slow it down without changing pitch, then loop the hard parts. Private and offline.",
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "storage"
  ],
  "host_permissions": [
    "*://*.youtube.com/*"
  ],
  "action": {
    "default_title": "Etude: show or hide on this page",
    "default_icon": {
      "16": "icons/icon-16.png",
      "32": "icons/icon-32.png",
      "48": "icons/icon-48.png",
      "128": "icons/icon-128.png"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "engine.js",
        "panel.js",
        "loop.js",
        "content.js"
      ],
      "css": [
        "panel.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "web_accessible_resources": [
    {
      "resources": [
        "signalsmith-stretch.mjs",
        "signalsmith-worklet.js"
      ],
      "matches": [
        "*://*.youtube.com/*"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "etude-extension@onurcelep.dev",
      "strict_min_version": "128.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}