JVC Professional APRIL 2007 NAB-2007 The ProHD Report
Copyright 2007 JVC Professional Products Company All rights reserved Page 31 of 43
Legacy HD CODECs are 10+ years old
Sony’s HDCAM camcorder was first delivered in the US in 1997, while the first
DVCPRO-HD camcorder was delivered in 2000. Together, these two formats have
been the foundation of the emergence of truly portable HD video acquisition,
however, the two CODEC technologies have now been eclipsed by newer, more
efficient compression algorithms.
In the mid-1990s, GOP (Group of Pictures) MPEG-2/4 compression technology was
not yet available, thus Sony and Panasonic had no option but to work with an intra-
frame DV implementations to accomplish portable HD compression for camcorders.
DV came from Motion-JPEG, adding bit stuffing to deliver CBR (Constant Bitrate
Recording) so the compressed DV could be recorded to constant linear velocity tape
within a video tape cassette. HDCAM was developed to record on ½” tape at a
bitrate of about 135Mbps video content, while DVCPRO-HD was a function of
Panasonic’s DVCPRO (25Mbps) format multiplied by 4, for a video content at
100Mbps, recording on ¼” tape at 4x DV linear tape speed.
There was only one way to get the bitrate down to a manageable level: bit-
reduction, pre-filtering, and sub-sampling. With today’s compression
technology, there is little need to compromise.
Fig. 16. HDCAM reduces the bandwidth prior to compression, down to
1440 pixels horizontally. The color sub-sampling is really 3:1:1 as the
CR & CB is only 480 pixels or 1/3 of the 1440. The number 3 in the
“3:1:1” is ¾ of 1920 (and of 4 as in “4:2:2”). 1440 horizontal pixels
come from a 4:3 aspect ratio HD image, corresponding to the 1920
pixels in the 16:9 image, both producing square pixels with the 1080
line format. HDCAM only comes in the 1080i flavor.