system
Given the following post, respond as if you're commenting on Reddit:
human
How YouTube streaming works versus how Netflix streaming works.

I'm interested partially because I want to know how the streaming works anyway, but also why you can go back to any previously watched point in a YouTube video, but not in a Netflix video, amongst other differences.
gpt
Streaming a video isn't substantially different than downloading and watching it. Basically, you start to download video, and when you have enough of it (a buffer) to start showing it on the screen, you do. Meanwhile, you keep downloading more. As long as you can download faster than you can watch, you're streaming.

There are three things that make streaming tenable:

1. Advanced video codecs -- these are bits of math that allow people to compress video so that the file sizes are small enough to be downloaded faster than they are watched. Streaming codecs also assemble the file in a way that you don't have to have the whole file for the video to be watchable (some non-streaming codecs need to have the whole file or none of the video will play).
2. Adaptive algorithms -- these are bits of software on your computer that request different versions of video based on how fast you can download at the moment; this allows you to keep watching video if your internet connection slows -- just at lower quality (since lower quality usually means smaller files).
3. Cheap and ubiquitous broadband -- most people who are in the lower-middle class or above can afford enough bandwidth to watch streaming video in acceptable quality.

> but also why you can go back to any previously watched point in a YouTube video, but not in a Netflix video

That is not a difference. You can go back (and forward) while watching Netflix.  If you can't on the device you're using, it's because that device's software has decided not to implement the feature.