Mp4 in RHEL 7, why won't it play

How do I get RHEL 7 to read mp4 files?

The video player is unable and neither can presentations in office libre. Google Chrome can. I have tried the EPEL, rpmfusion , and rpmforge repositories, but am going in circles and worry about jeopardizing integrity of system.

Would appreciate hearing what others have tried. Any guidance would be appreciated.

Thank you!

Dan