@Ramesh, Thee are several director's viewfinder type apps. Of course, they can't simulate the same optical properties of the larger sensor in HD (and cinema, especially) cameras. The app can simulate the AOV/FOV, but will not be able to account for or represent many wide FOV situations for focal lengths shorter than what is possible on the camera. It can be pretty restrictive. :(

@Michal, I believe iSee4K has been pulled since it's no longer being developed/supported.