Youtube サムネイル画像の取得

Youtube動画URL
https://www.youtube.com/watch?v=動画ID

120 × 90 [default]
http://img.youtube.com/vi/動画ID/default.jpg

120 × 90 [ 1 ]
http://img.youtube.com/vi/動画ID/1.jpg

120 × 90 [ 2 ]
http://img.youtube.com/vi/動画ID/2.jpg

120 × 90 [ 3 ]
http://img.youtube.com/vi/動画ID/3.jpg

320 × 180
http://img.youtube.com/vi/動画ID/mqdefault.jpg

480 × 360
http://img.youtube.com/vi/動画ID/hqdefault.jpg

640 × 480
http://img.youtube.com/vi/動画ID/sddefault.jpg

1280 × 720
http://img.youtube.com/vi/動画ID/maxresdefault.jpg