Video Player Definiton

A video player is a kind of media player for playing back digital video data from media such as optical discs (for example, DVD, VCD), as well as from files of appropriate formats such as MPEG, AVI, RealVideo, and QuickTime.
In addition to VCR-like functions such as playing, pausing, stopping, rewinding, and forwarding, some common functions include zooming/full screen, audio channel selection, subtitle selection, and frame capturing.
Many of the video players also support simple playback of digital audio and 3D playback of 2D video.

3D Video players are used to play back 2D video in 3D format.

A high-quality three-dimensional video presentation requires that each frame of a motion picture/video be embedded with information on the depth of objects present in the scene. This process involves shooting the video with special equipment from two distinct perspectives or modelling and rendering each frame as a collection of objects composed of 3D vertices and textures, much like in any modern video game, to achieve special effects. Tedious and costly, this method is only used in a small fraction of movies produced worldwide, while most movies remain in the form of traditional 2D images.

It is, however, possible to give an otherwise two-dimensional picture the appearance of depth with a much more simple approach. Using a technique known as anaglyph processing a "flat" picture can be transformed so as to give an illusion of depth when viewed through anaglyph glasses (usually red-cyan). An image viewed through anaglyph glasses appears to have both protruding and deeply embedded objects in it, at the expense of somewhat distorted colours. The method itself is old enough, dating back to mid-19th century , but it is only with recent advances in computer technology that is has become possible to apply this kind of transformation to a series of frames in a motion picture reasonably fast or even in real time, i.e. as the video is being played back. Several implementations exist in the form of 3D video players that render conventional 2D video in anaglyph 3D, as well as in the form of 3D video converters,that transform video into stereoscopic anaglyph and transcode it for playback with regular software or hardware video players.
From wikipedia