The Oculus Rift has a feature called Asynchronous Spacewarp. In short, this feature is used when games temporarily dip below the 90fps threshold and it works essentially by adding in fake extra frames.
This is great for games to not lose immersion, but when you are watching video you lose frames pretty often, for example when you forward in the video or switch to another one. And if you play a video that your computer can’t handle, then Asynchronous Spacewarp might turn on and not turn off until a full restart of the Oculus UI.
When AS is on, you will experience ghosting, uneven framerates and in fact, your computer might not be able to play videos it previously could because AS itself adds non-trivial GPU performance bottlenecks.
To turn off AS
Find the file C:\Program Files\Oculus\Support\oculus-diagnostics\OculusDebugTool.exe and start it.
Under “Asynchronous Spacewarp”, select “Disabled”. The setting will need to be reapplied every time you reboot your computer.