Because that system (laptop) I'm going to buy has a N4000 Celeron processor with 4 GB of RAM as well as a SSD plus a Win 10 S.
I mean smooth playback is possible on YouTube and through VLC player or any media player?
My sole purpose at getting a new system is for playing/viewing/watching 1080p, 2K & 4K content online (YouTube) or video files on VLC type of video players.
CPU supports 4K resolution:
Now, how the playback will behave is something that depends on other factors: System integration, laptop limitations due to design, thermal design, internet speed and bandwidth. I would be more concerned about the RAM, 4GB I think is short... Nowadays, just launching Google and opening few tabs can take 1GB RAM or more....