Can you give us some information about the system, software and apps?
Which graphics card, Operating system, are you using DeoVR from Steam, Oculus?
Can you check if the settings in SteamVR has Smoothing disabled?
Do you have the K-lite pack installed?
Which video format and resolution are you using / are you having this issue with?
Can you try playing the video in the Windows app 'Movies & TV' / 'Movies & Films' or whichever it would be in your local language? - This app comes by default with Windows, you should already have it on your system.
Do you have the same issue when playing it with Movies & TV app?