system
Given the following post, respond as if you're commenting on Reddit:
human
eli5: Why are video file sizes so small?

A normal image stored on a phone is around 5 mb, if you calculate that way, a 1080p 60 fps video should be 60 frames X 5 mb X 600 seconds = 180000 MB= 180GB. But if you check a file size of an actual 10 minute video, it is only around 1GB. How can it be so small?
gpt
Video compression. The video file doesn’t store every frame, it just stores what changes between frames. 

Periodically there will be a full frame, called a “key frame”, just to reset everything but most of the “frames” in the file are just a small list of changes from the prior frame. Unless there’s a jump cut, there is usually very little difference between adjacent frames. 

Basically, the video file isn’t the video, it’s instructions to the software on how to recreate the video in real time.