Vie Fit is the Bluetooth true wireless earphones which share the audio between the device and two earphones. This wireless audio sync requires a buffering. When you are watching the video, this may cause the delay of the audio.
If the video and the audio sync is more than the slight delay, the most frequent cause of the issue is the audio streaming. Please try the followings and see if it improves.
1: Shut down the unnecessary application.
2: Restart your device.
3: Download the video before watching (If possible).