Sierra?

Mac OS X

Release Date: Oct 5, 17

Your OS is up to date

Keeping your operating system up-to-date ensures you qualify for the latest software updates necessary for optimal media playback.

Buffering occurs when the media you're viewing has played out faster than your device can download it, causing it to stop and wait for the next chunk of data to become available.

Buffering is an issue specific to your internet connection, and not the speed or capability of the device you're viewing on.