(Image size depends on video.)
-
Player Background Thumbnail (480x360 pixels)
http://img.youtube.com/vi/<insert-youtube-video-id-here>/0.jpg -
Start Thumbnail (120x90 pixels)
http://img.youtube.com/vi/<insert-youtube-video-id-here>/1.jpg -
Middle Thumbnail (120x90 pixels)
http://img.youtube.com/vi/<insert-youtube-video-id-here>/2.jpg -
End Thumbnail (120x90 pixels)
http://i1.ytimg.com/vi/<insert-youtube-video-id-here>/3.jpg -
High Quality Thumbnail (480x360 pixels)
http://i1.ytimg.com/vi/<insert-youtube-video-id-here>/hqdefault.jpg -
Medium Quality Thumbnail (320x180 pixels)
http://i1.ytimg.com/vi/<insert-youtube-video-id-here>/mqdefault.jpg -
Normal Quality Thumbnail (120x90 pixels)
http://i1.ytimg.com/vi/<insert-youtube-video-id-here>/default.jpg
And additionally, the next two thumbnails may or may not exist. For HQ videos they exist.
-
Standard Definition Thumbnail (640x480 pixels)
http://i1.ytimg.com/vi/<insert-youtube-video-id-here>/sddefault.jpg -
Maximum Resolution Thumbnail (1920x1080 pixels)
http://i1.ytimg.com/vi/<insert-youtube-video-id-here>/maxresdefault.jpg -
1st Thumbnail Image, Small (120×90)
http://img.youtube.com/vi/bQVoAWSP7k4/1.jpg3rd Thumbnail Image, Small (120×90)
http://img.youtube.com/vi/bQVoAWSP7k4/3.jpg2nd | Default Thumbnail Image, Small (120×90)
http://img.youtube.com/vi/bQVoAWSP7k4/2.jpgDefault Thumbnail Image, Full-Size (480×360)
http://img.youtube.com/vi/bQVoAWSP7k4/0.jpg
