Examine source code of Soporific Player

{
  "manifest_version": 2,
  "name": "Soporific Player",
  "version": "1.0",
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/watch*"
      ],
      "js": [
        "extension.js"
      ],
      "run_at": "document_start"
    }
  ]
}