Hi Fifiring,
Thanks for giving those steps a try.
To confirm, this is only happening when you record a video with the Camera app, and then playback that video?
Does it happen playing videos in other apps?
Have you tried to force your Camera and Photos apps to close and restart your iPhone?
Try these steps here:
How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support
Restart your iPhone, iPad, or iPod touch - Apple Support
If the issue with recording continues, I recommend reaching out to Apple Support to further isolate and resolve this issue:
Contact - Official Apple Support
Good luck!
Thanks for using the Apple Support Communities.