The video, obtained by WABC-TV, was filmed by a witness late last month but not revealed until now. Police have already seen it, WABC-TV reports.
"What the f**k is wrong with you?" shouts one of the bikers, as Lien is pulled from his Range Rover, which contain his wife and 2-year-old daughter.
The video appears to show the bikers beating Lien with their helmets and stomping on him. At one point Lien is shown lying on the ground, not moving.
WARNING: Video is violent and may be unsuitable for some viewers.