Is there already a mod where it automatically normalizes the volume of the videos? Some of the videos are very silent, while some are very loud since they all come from different sources.

Most of the mods here are Japanese so I have no idea if it's already made or not.

you can adjust video volume by using mouse wheel when playing a score. You can see green line on the bottom of the screen when you stir your mouse wheel
Note:
-The max volume video is 200
-Sometime on volume 110 - 120 can be very sensitive (ex: 110 volume is too low, when 115 volume is too loud)

About your question, i guess there isn't any mod like that for now.

Correct me if i was wrong.

Guess no one's gonna correct you, which is sad. I'm already aware of the whole Mouse Scroll on the video thing, but it all feels manual and sometimes some videos don't even respond to it which is annoying.

Not a mod suggestion or anything but I didn't know about manually adjusting the volume with the scroll wheel, I ended up downloading different videos and adjusting the latency lol