YouTube Auto-Generated Thumbnails

YouTube generates thumbnails for each video, these are in various sizes as follows;

Default – 120×90 http://img.youtube.com/vi/<video-id>/default.jpg

Small x4 – 120×90 http://img.youtube.com/vi/<video-id>/[0-4].jpg

Medium – 320×180 http://img.youtube.com/vi/<video-id>/mqdefault.jpg

High – 480×360 http://img.youtube.com/vi/<video-id>/hqdefault.jpg

Maximum – 4k, 1080p, 720p http://img.youtube.com/vi/<video-id>/maxresdefault.jpg