Roll Special

How make a double roll charcter in a scene?

can u tell me,in a scene of t.v or film a one charcter do the double roll in one scene. how is possible ?and whose type of special effect use?

role, not roll
In film and older video tape technology, it is done by making a mask that covers one side of the scene leaving the image black (and the film negative clear) The actor does the scene as one character, perhaps with a stand in providing timing of lines and positioning for the other character. Then the actor dresses for the other role, the mask is moved and the other scene is shot, perhaps with a recording of the first scene so the actor can more smoothly respond to the words. The two scenes are merged in the printing process. In the first version of “The Parent Trap”, http://www.imdb.com/title/tt0055277/ if you look carefully when both twins are in a scene you can find the line of the mask edge – it often is lined up with vertical lines in the scene like a bookcase. When camera shots show the back of one character’s head, that is a standin and the shot is done in a single pass. Again the actor has to take both rolls and shoot the scene twice as the camera looks at one face and then the other, but that reshooting is done with multiple actors anyway for closeups, etc.
In modern work the actor works against a green screen and computers merge the background and the actor’s characters.
In some old TV work, the scene was shot with one character and background and that tape used as background for a live video shot of the other character (when video tape merging was very complicated but mixing live and background was not)

REO Speedwagon – Roll With The Changes [HQ] (Live Midnight Special 1978)