Video is the primary media in the MCL. Video is a sequence of the still image frames. It may link with an audio sequence. When these frames display on the screen as a continuous stream, it generates the animation. The frame sequence is numbered from 0 to n.

A video may be compressed in certain format such as MPEG. The procedure of video playback starts to read from a source, split video and audio, decode data, and render to window. A media source may be a file in a CD-ROM or on the Internet. Video and audio are split into different decoders and they are synchronized by a clock. The output frame is rendered onto a window.

MCL commands can control the video playback. It can also complete video transform together with an image or a 3D mesh input. A transform can generate special visual effects. For example, fade transform can show a video fade smoothly from a frame to another image. These transforms make video playback more like a film. In the Star War movie, the wipe and fade transforms are widely used to generate the sepcial visual effects. MCL provides simple methods to do this.

• Open Video

  Command	_video argument
  Argument	name=video_file_name
  Descriptiotn	open a video file specified by name. The default file name is default.mpg if there is no argument. The curly braces {} will group the string as one argument. The "" will also group the string and allow the name to be a variable.
  Examples	_video {name=default.mpg} # other commands video_

• Close Video

  Command	video_
  Argument	none
  Descriptiotn	close a video file which is opened by _video.
  Examples	_video {name=default.mpg} # other commands video_

• Get Video Information

  Command	?video argument
  Argument	capability get the list of video capability; type get the video type; current get the video current frame; start get the video start frame; end get the video end frame; length get the video frame number;
  Descriptiotn	?video command get the information about the video. Its argument specifies the item of the attribute. capability item maybe a list with one or more elements of AsynchronousStream, HasClock, and SupportSeek. AsynchronousStream indicates that the video is an asynchronous stream; HasClock indicates that there is a clock for the video; SupportSeek indicates that the video supports random seek. format item returns video format such as MPEG, DVD, and so on. type item get the info if the video is STREAMTYPE_READ for readable, STREAMTYPE_WRITE for writeable, or STREAMTYPE_TRANSFORM for transformable. The current, start, and end returns the current, start, and end frame of the video. Video position is numbered as frame. length gets the total video frame number.
  Examples	_video {name=default.mpg} set caps [?video capability] video_

Snap is an abstraction of a snapshot of a picture or a video frame. It maybe an image, a texture, a 3D mesh, or a frame of a video. It is an input for a transform.

• Snap Command

  Command	_snap argument
  Argument	image=image_file_name; default value default.png mesh=mesh_file_name; default value default.msh
  Descriptiotn	argument is the list of attributes. If argument is empty, the sanp is get current frame of the video. image=filename specifies the image file to be used. mesh=filename specifies the mesh file to be used.
  Examples	_snap {image=default.png}