I've noticed on Youtube they seem to buffer really popular videos really well, things like Gangnam Style when it was being played probably to tens of thousands

I've noticed on Youtube they seem to buffer really popular videos really well, things like Gangnam Style when it was being played probably to tens of thousands of simultaneous users were surprisingly good - I think they have some sort of really good buffered caching or something. I suspect they might do the same with adverts that they know will stay the same and know they will serve to many users. The disconnect is there for many videos where a perfectly buffered ad precedes a slow buffering video or something, but they seem to use that technology on some user videos too I think - or something similar.