system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do videos need to buffer when I rewind?

It doesn't make any sense to me. I just watched it so shouldn't the clip be saved on my computer? Why do I need to download it a second time?
gpt
Depends on how the buffer is implemented.


Some streaming videos only buffer the 10-30 seconds you're about to watch next and don't save anything to your computer. This is popular for content where licensing might be an issue, because it's more like an on-demand broadcast, and they're not providing you with an actual offline copy of the video.


Sites like YouTube usually do use actual video files that are played inside the browser using Flash or HTML5, and these should allow you to rewind without having to download the data again. However, this is only true as long as you don't skip ahead. If you watch the first 3 minutes, then skip ahead to 10:00, the player will start a new download (beginning at 10:00) and discard the old data (0:00-3:00). If you then go back to say 2:00, the player will not find any buffered data.