Initially, moving pictures meant only the movement that is perceived when a string of celluloid-recorded images are projected at a rate of about 16 or more frames per second (see persistence of vision). Today, motion pictures (or "movies") are an art form, as well as one of the most popular forms of entertainment.
Most films shown in the United States are rated under a voluntary rating system instituted by the Motion Picture Association of America:
A feature film is usually defined as being more than 60 minutes in length.
Opportunities to see a feature film include:
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Originally moving picture film was shot at various speeds using hand-cranked cameras; then the speed for mechanized cameras and projectors was standardized at 16 frames per second, which was faster than much existing hand-cranked footage. A new standard speed, 24 frames per second, came with the introduction of sound. Improvements since the late 1800s include the mechanization of cameras, allowing them to record at a consistent speed, the invention of more sophisticated filmstocks and lenses, allowing directors to film in increasingly dim conditions, and the development of synch sound, allowing sound to be recorded at exactly the same speed as its corresponding video. Since the advent of many other media technologies, film may include a broad range of media--both linear and non-linear, dramatic and informational, motion and still (though progressive).