What's the algorithm using in this video buffering?

Recently I've watched a lot of online courses and I just noticed that some of the video my course video are buffering in a strange way which is differ from I used to know on YouTube:

(The vertical bar on the right hand side is dis-continuous.)

While on YouTube: (The buffering is continuous and appended after the time I paused.)

So what's the name of algorithm used in the first one?

https://stackoverflow.com/questions/67400894/whats-the-algorithm-using-in-this-video-buffering May 05, 2021 at 08:02PM