35mm film

Thirty five millimeter film is the professional standard format for image storage and projection.  

Ample area for optical and relatively high speed of film assures good audio response. Runs at 18 inches/sec (18 frames/foot), 35 mm magnetic film can hold as many as 6 tracks of audio.

Often the optical tracks on the projection print (2) are encoded via the Dolby Surround process (or similar systems such as UltraStereo) which permits 4 somewhat discrete channels: Centre, Left, Right and Surround/rear.  

Film may also contain digital audio information as well.