Again, do some research via Google. There is bound to be a website. Just look at what id recommended. What kind of mags are you going to get for your GBBR? Once you know this then research to see how to properly load it with gas and how long it will last.
Only once you cannot find this information yourself, then come to the forums with what you have learned and what you still need to know. For most stuff, you don't need to do this cause you will mostly find what you need someone on the internet or on the forums already.
Also you talk about this video. You realize each mag has its own gas capacity therefore he can reload with a different mag and keep shooting right? Same as a pistol. So if he has 10 mags of course he can keep shooting cause theres gas in all of them.