need wifi for video play
Why can't I play my videos on iPhone 8 without requiring an Internet connection?!?
iPhone 8, iOS 12
What kind os videos? Videos that you shot on your iPhone?
Maybe you uploaded them to iCloud, that is why they need to be downloaded on the device to play.
Check the settings under Settings > Photos and see if 'Optimize iPhone Storage' is enabled. If so, then your videos are storing in iCloud. To play them, you have to download the first, or select an option to keep originals on the device.