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Pre-rendering is the process in which video footage which is not being rendered in real-time by the hardware that is outputing or playing back the video. Instead, the video is a recording of a footage that was previously rendered on a different equipment (typically one that is more powerful than the hardware used for playback). Pre-rendered assets (typically movies) may also be outsourced by the developer to an outside production company. Such assets usually have a level of complexity that is too great for the target platform to render in real-time.

The term pre-rendered describes anything that is not rendered in real-time. This includes content that could have been run in real-time with more effort on the part of the developer (e.g. video that covers a large number of a game's environments without pausing to load, or video of a game in an early state of development that is rendered in slow-motion and then played back at regular speed). The term is generally not used to describe video captures of real-time rendered graphics despite the fact that video is technically prerendered by its nature. The term is also not used to describe hand drawn assets or photographed assets (these assets not being computer rendered in the first place).

Advantage and disadvantage

The advantage of pre-rendering is the ability to use graphic models that are more complex and computationally intensive than what can be rendered in real-time, due to the possibility of using multiple computers over extended periods of time to render the end results.

The disadvantage of pre-rendering, in the case of video game graphics, is a generally lower level of interactivity, if any, with the player. Another negative side of pre-rendered assets is that changes cannot be made during gameplay. A game with pre-rendered backgrounds is forced to use fixed camera angles, and a game with pre-rendered video generally cannot reflect any changes the game's characters might have undergone during gameplay (such as wounds or customized clothing) without having an alternate version of the video stored. This is generally not feasible due to the large amount of space required to store pre-rendered assets of high quality. However, in some advanced implementations, such as in Final Fantasy VII, real-time assets were composited with pre-rendered video, allowing dynamic backgrounds and changing camera angles.

Another problem is that a game with pre-rendered lighting cannot easily change the state of the lighting in a convincing manner.

Usage

One of the first games to extensively use pre-rendered graphics and full motion video was The 7th Guest. Released in 1992 as the first personal computer game exclusively on CD-ROM, the game was hugely popular, although reviews from critics were mixed. The game featured pre-rendered video sequences that were at a resolution of 640x320 at 15 frames per second, a feat previously thought impossible on personal computers. Shortly after the release of Myst made the use of pre-rendered and CD-ROMs even more popular.