User Guide

304 Appendix E, Digital Compression
Inverse Telecine
Frame redundancy is an area in which preparation prior to encoding can improve the
resulting MPEG-2 video. When film (24 fps) is transferred to NTSC video (30 fps), fields must
be added to bring the 24 fps material up to 30 fps. This is done by duplicating fields and is
called the telecine process.
During the telecine process, individual frames of film are duplicated at regular intervals
during the 3:2 pull-down process. Two fields derived from film frame A are followed by three
fields from film frame B, and so forth, and two video fields are derived from each frame of
film. The ordering of fields is alternated, resulting in a unique pattern that repeats every five
video frames.
MPEG-2 decoders, such as those on DVD players, have the ability to function with 24 fps
MPEG video streams, turning them back into 29.97 video on output. This unique property of
converting 24 fps MPEG-2 video back into 29.97 video means that before encoding, 29.97
video can be turned back into the original 24 fps film frame sequence. This removal, called
inverse telecine, has several benefits: it eliminates redundant fields, allowing the
compression system to allocate more bits to the remaining unique frames, and eliminates
encoding artifacts resulting from motion between fields in a single frame.
24 frames on
original film
Converted to
30 frames on
video
Redundant fields are removed prior
to MPEG encoding
Video Frames