[TZubiri]

There's many cases where server side takes you 98% there, but it still makes economical sense to spend shitloads on getting that 2% there.

In this case it's not the same whether your server sends a 10 second packet and the viewer views all of it, and whether server sends a 10 second packet, but client pauses at the 5s mark (which needs client-side logic)

Might sound trivial, but at netflix scale there's guaranteed a developer dedicated to that, probably a team, and maybe even a department.