Standard sound aperture (reduced frame):

Code a (007/04 - motion picture) indicates that the motion picture has a standard sound aperture (reduced frame).  It is used for non-wide-screen formats, for example, for all standard sound 35 mm., 16 mm., and super 8 mm. film.  Code a should be used even for silent films in which a space has been left for the inclusion of a sound track, that is, where a full frame silent picture has been cropped to allow space for a sound track.