Without knowing the specs of your computer, I’d still be willing to bet that your computer is the problem. Defrag your hard drive, close as many unused apps as possible. Is this a Windows PC or a Mac? How old is it? MP4s should have no problem running on any machine built since 2010.
Try taking a copy of the video on a USB 3.0 flash drive to another computer with USB 3.0. If it plays well on that machine, then your PC has resource issues.
