DVD Demystified

370
Advantages of DV over DVD-Video
Chapter 8
Capacity. D-VHS has a much greater capacity than DVD (and DV), with
a digital tape holding almost 50 gigabytes of data. Even though the real bit
capacity of DV is significantly higher than D-VHS, DV tape is narrower.
Recordable. As with VCRs, this is the difference that makes all the difference.
The high compression required by DVD-Video makes it an unsuitable
candidate for shooting and editing. Recordable DVD more likely will
be the final destination of digital video files from DV cameras and editing
systems. Since it is possible to store DV-format (I-MPEG) video on a DVD-
ROM, this may become popular for quick-access archiving. D-VHS can
record from a digital source, but a digital decoder also must be available for
playback.
Editing. A significant advantage of DV is that each frame is compressed
individually, so they can be inserted, deleted, and combined in any order.
This is especially useful for nonlinear digital editing systems. Because
DVD’s MPEG-2 P and B frames rely on nearby frames, they must be decompressed
and recompressed to make an edit within a group of pictures. This
can degrade picture quality.
Video. DV uses the same component digital format as DVD-Video, the
only difference being the sampling system. DV uses 4:1:1 sampling for
NTSC and 4:2:0 sampling for PAL. DVD-Video uses 4:2:0 sampling for both
NTSC and PAL. Both sampling methods record the same amount of information
but in slightly different ways, and the arguments are endless over
which is better. DV’s I-MPEG compression removes much less information
than DVD’s MPEG-2 compression but is correspondingly less efficient. DV
video quality is superior to DVD’s average video data rate of 3.5 Mbps but
is not noticeably different when DVD rates are increased to more than 5 or
6 Mbps. D-VHS can record a digital video bit stream at up to 28 Mbps,
which is more than adequate for even high-quality digital video formats
such as those used for HDTV.
Price. D-VHS tapes may cost more than DVD discs, even more than
recordable discs in the long term, but they are much more cost-effective
when measured in price per gigabyte.