Advertisement
A new generation of video compression.
Compression technology is the secret that makes possible much of today's consumer
digital entertainment. In the professional studio, uncompressed Standard Definition
video requires 168 million bits per second (Mbps) and High Definition requires 1.2 billion
bits per second (Gbps). DVDs and HDTV broadcasting would have been unthinkable
without MPEG-2 compression technology to bring these massive data rates down to a
manageable size. While MPEG-2 technology dates from the 1990s, several recent advances
can achieve even higher quality at lower data rates. These advances have been built into
a new standard with the somewhat awkward name: "MPEG-4 AVC / H.264."
DV and intra-frame compression.
repetition from the video signal. For example, one pixel of blue sky is almost identical
to the pixel next to it. Intra-frame compression, as used in the DV (digital videocassette)
format, recognizes these patterns and reduces the data accordingly.
MPEG-2 and inter-frame compression.
and adds a second level of compression: inter-frame. Inter-frame compression works
because the typical video frame is almost identical to the frames before and after. By
encoding only the differences between certain frames, MPEG-2 compression can achieve
another round of bitrate reduction. The result? Very high quality at far lower bitrates
than intra-frame compression alone.
Compression works primarily by removing
MPEG-2 starts with intra-frame technology
A
Intra-frame compression works because
one pixel of blacktop is almost exactly the
same as the pixel next to it.
A
B
Inter-frame compression achieves another
round of bitrate reduction by taking
advantage of the major similarities
between one frame and the next. Here
the background (A) remains largely the
same while the car (B) changes.
A
Advertisement
