system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do different video formats change the size of a video, even at the same resolution and frame rate? Isn’t it the same video you’re watching?
gpt
There are two things that you can tweak.

The first is the compression algorithm. This will be things like MPEG versus h.264 or h.265 algorithms. They describe how to strip down the video file to as few elements as possible to reproduce it later. Essentially, you trade storage time for CPU time to compress/decompress it.

The second is the lossy factor. Most video compression formats do not attempt to serve back the exact same set of pixels. Instead, you get something that is good enough to be recognizable on the other end. Of course, the amount of detail you want to keep is an adjustable factor in the compression algorithm. You can take the same source video and throw it into the same algorithm with two different settings and get different quality video out the other end.