While IE9 does support HTML5 <video> tags, it fails to work until you force HTML5 mode.

Rails Long Term Support

Rails LTS provides security patches for old versions of Ruby on Rails (2.3, 3.2, 4.2 and 5.2)

Option 1: Doctype

Make sure your HTML document uses HTML5. It should start like this:

<!DOCTYPE html>

If you can not set a doctype, you use the X-UA-Compatible meta tag in your HTML <head>.

<meta http-equiv="X-UA-Compatible" content="IE=Edge"/>