How do I Force YouTube to always buffer the entire video before playing?

Hey!! can you help me??

When I'm watching a YouTube video it will only buffer the next 30 seconds or so. This is something I want to avoid because when trying to watch 1080p videos it will keep pausing because it has to download the next 30 seconds and my connection isn't fast enough to keep up.

I'd rather it download the entire video before I can click play. But whenever it does this there doesn't seem to be a way to get it to do what I want.

I understand that they did this to save bandwidth. But it would be better if they would at least make it an option. Like being able to click a button that tells them "hey, I'm planning on watching this entire video so download the whole thing".

It seems to be random too. It happens in some 1080p videos, not in others, in some 720p videos, not in others. And it's been happening more recently in the past 2 months.

One last thing I have a Mac and this happens with Safari web browser only!

Thanks in advance, 10 points at stake! <:)