Youtube video details are stored in the byId object inside videos

youtube-watch-details-with-video-details.json

{
  "api": {
      "libraryLoaded": false
   },
   "videos": {
      "byId": {
        "FLqvTE1Eqfg": {
         "kind": "youtube#video",
         "etag": "\"XI7nbFXulYBIpL0ayR_gDh3eu1k/rzYqHJdz-a40clbPa3V5RJul7XU\"",
         "description": "here is the description we just loaded",
         "...": "..."
      },
      "mostPopular": {
        "items": ["FLqvTE1Eqfg", "..."],
        "totalResults": 200,
        "nextPageToken": "some-cryptic-token"
      },
      "categories": {
	 "1": "Film & Animation",
	 "2": "Music"
      },
      "byCategory": {
        "1": {
          "totalResults": 200,
          "items": ["..."],
          "nextPageToken": "some-cryptic-token"
        }
      }
   }
}