i.ytimg.com/vi/u_tGHnEMqKc/maxresdefault.jpg

thumbnail link doesn't work in all cases - Stack Overflow

All about Thumbnail Images as ytimg maxresdefault

] `maxresdefault` doesn't exist sometimes · Issue #340 · yt

の動画のサムネイル取得が思った以上に簡単だった件

php - Fetch highest thumbnail resolution - Stack Overflow

All about Thumbnail Images as ytimg maxresdefault

i.ytimg.com/vi/vGCAzFvA8ik/maxresdefault.jpg, leg slides

i.ytimg.com/vi/I4j4OGl_XHQ/maxresdefault.jpg

の動画のサムネイル取得が思った以上に簡単だった件