Whilst Bein's might not be sophisticated and probably is a bit of guesswork. Im.surprised its not possible with technology that is available today.I think bein sports used a technology called guesswork.
Given semi automated offside can track several moving human body parts and then present that back in a 3d image to definitively prove (margin of error aside) the position of the players the doing the same with a ball and a static line ought to easily be in reach.