This is applicable to all the realme devices.
Mobile phone camera recording video no sound solution:
1. Please make sure the phone settings - sound and vibration - the media volume is turned on.
2. If it is invalid, try again to shoot a video.
3. Please backup the phone data, restore the factory settings or re-flash the firmware version to rule out the system is abnormal.
If the above steps do not solve your problem, please go to the nearby realme service center for testing.