Video Synchronization
Richard Brice28.1 Introduction
Audio, for all its artistic power and technological intricacy, is just one element in today’s
multimedia entertainment phalanx. Today’s recording engineers are more likely to fi nd
themselves working in a MIDI studio locked to SMPTE time code than they are to be
rigging microphones. Today’s composer has a better chance of making his/her living
by proactively seeking work for television and fi lm (for which he/she will require an
understanding of the medium) than to wait for a commission for a symphony from a rich
patron! This chapter contains a description of the principles and concepts that form the
technical foundations of an understanding of analogue and digital television.
28.2 Persistence of Vision .............................................................................................
The human eye exhibits an important property that has great relevance to the fi lm and
video industries. This property is known as the persistence of vision. When an image
is impressed upon the eye, an instantaneous cessation of the stimulus does not result
in a similarly instantaneous cessation of signals within the optic nerve and visual
processing centers. Instead, an exponential “ lag ” takes place with a relatively long time
required for total decay. The cinema has exploited this effect for over 100 years. Due
to the persistence of vision, if the eye is presented with a succession of still images at a
suffi ciently rapid rate, each frame differing only in the positions moving within a fi xed
frame of reference, the impression is gained of a moving image. In a fi lm projector
each still frame of fi lm is drawn into position in front of an intense light source while
the source of light is shut off by means of a rotating shutter. Once the fi lm frame has
stabilized, the light is allowed through—by opening the shutter—and the image on the
CHAPTER 28