system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do the videos from the early 1900's look like they are being played at 2.5x speed?
gpt
The original hand cranked cameras like the pathé and the bell & Howell 2709 had what was called an 8:1 gear ratio, which meant for every 360 degree crank it would produce 8 frames. 

There was a song that cameramen would sing as they handcranked, which would result in about two revolutions per second - 16 frames. It would fluctuate, obviously, and sometimes cameramen would deliberately change their cranking speed depending on the scene. 

Projectors were also handcranked in the early days, and the projectionist would change his/her speed depending on the scene. 

With the advent of sound, the speed of recording /playback was deliberately changed to 24 frames per second to help with the fidelity of sound. 

A proper silent film should be played back at 16/18 frames per second, and some criterion versions were transferred that way.