Difficult to diagnose since the issue could be on either side of the wall. I'd guess YouTube's CDN's and/or differences in requested formats (WebM/AV1 vs. mp4/h264).
It could be YouTube using a global Content Delivery Network (CDN), which are servers all over the world caching (having a copy) of the videos. They've got limited space, and thus only room for the most popular videos. Every video is available in various qualities (360p, 480p, etc.), and I can imagine a scenario where the 360p video is stored "centrally" while the 720p/1080p versions are spread around the difference caches for easy access.
I've experienced up to a minute of load-time on some of my older, obscure, never-watched decade old uploads.
Difficult to diagnose since the issue could be on either side of the wall. I'd guess YouTube's CDN's and/or differences in requested formats (WebM/AV1 vs. mp4/h264).
It could be YouTube using a global Content Delivery Network (CDN), which are servers all over the world caching (having a copy) of the videos. They've got limited space, and thus only room for the most popular videos. Every video is available in various qualities (360p, 480p, etc.), and I can imagine a scenario where the 360p video is stored "centrally" while the 720p/1080p versions are spread around the difference caches for easy access.
I've experienced up to a minute of load-time on some of my older, obscure, never-watched decade old uploads.