Every thumbnail the official Data API v3 declares for one YouTube video (videos.list, 1 quota unit, 1 credit), one item per size: id is the size name, metrics carries width and height. Only the sizes that video actually has are returned — no URL is ever built from a filename convention, so a size that is missing is absent rather than a guessed link. Nothing else about the video comes back.

Every thumbnail the official Data API v3 declares for one YouTube video (videos.list, 1 quota unit), one item per size: id is the size name (default, medium, high, standard, maxres) and metrics carries width and height. Only the sizes that video actually has come back -- NO url is ever built from a filename convention, so a size the response did not declare is absent rather than a guessed link that may 404. Nothing else about the video is returned: title, duration, views and likes are youtube/video.