MP4 videos are the animated things I make.
I am surprised to hear this.
Usually the I-Pad has problems playing a mp4.
The I-Pad sucks for playing anything.

So there is something wrong with it if your Chromebook won't play it.

You need to run it through this video converter to clean it up.

https://video.online-convert.com/convert-to-mp4

Here are some of my MP4's, can you play them?

https://www.geocities.ws/bkbrat/mp4/