This invention directs to a video/motion picture displaying apparatus for viewing via 3D spectacles with an internal 3D synchronizing unit including an image capturing means, a synchronizing means to identify synchronization events according to a set of synchronization rules, and a transmitting unit. It further directs to a 2D video/motion picture embedded with synchronizing signals produced with the same synchronization rules. The invention also discloses a 3D synchronizing signal composing/embedding device for embedding synchronizing signals to a 2D video/motion picture including a data capturing means, a converting means, a synchronizing means and a composing means or an embedding means. It also teaches a related 3D control device configured to acquire and utilize the embedded synchronizing signals to control the transmission of light of the 3D spectacles.