Buffering is usually either the result of a slow internet connection or an underpowered streaming device.
You can reduce buffering when streaming video by reducing the video resolution. A video playing in 720p will require a lot less data than a video playing at 1080p. Most video players allow users to manually adjust the resolution.
Make sure your base internet speed is fast enough to stream the resolution you want to watch. 10 Mbps is usually good enough for 1080p HD, and 25 Mbps is needed for 4K UHD.
A VPN will slow your connection somewhat, but all of the VPNs we recommend should offer sufficient bandwidth for HD streaming.
Check to see no other programs on your device or devices in your household are sapping available bandwidth.
If you have an underpowered device, it won’t be able to decompress the video fast enough to play without stopping to buffer. And if you’re using a VPN, then the device will also have to decrypt the video stream as it downloads, adding a further burden and causing more buffering.