1
Is this problem affecting all video files, or just one specific video file?
2
If you are using the new Media Player app to play the video file, open the Settings App.
Go to Apps - Installed Apps.
Scroll down to find the Media Player app.
Select that app and choose Advanced Options.
Perform the Repair option and the Reset option on that app.
Then check if you can play the video file.
3
If that does not resolve the problem, right click the video file in File Explorer and select Properties.
Please provide a screenshot of the resulting Properties dialog box.