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RE: [AV Media Matters] SVHS Correction & Preservation
Jim, I think I need to clarify my previous post, as I was referring to
storage of video in DV format as a master, not DVD-Video. I was
thinking along the same lines as audio, where masters are generally
stored as WAV files and listening copies as CD-A, and did not think to
clarify.
I realise that the DV format is lossy and that is one of the reasons we
have not yet committed. However, DV compression works differently to
MPEG and is far superior. My understanding of DV compression is that it
does not result in a loss of detail, but a loss of some colour
information per four-pixel block. Also, there should be no artifacts
unless copying from digital tape where there are dropouts on the tape or
the tape has deteriorated, so this should not be an issue in the case of
DVD.
The downside of staying with analogue is that every transfer is one
further generation from the original. Also, every time analogue media
is played the quality of the content deteriorates that little bit
further. Time is also a crucial factor that is seldom fully calculated
in the cast of transfer. This is not the case with digital, as every
copy should be an exact replica of the original and can be made in a
matter of minutes.
Stability has not been proven for any digital media, as none have been
around long enough. That is why I suggested creation of backups as an
ongoing protection measure. This could even be extended to include
migration to newer and better digital formats as they become available.
Finally, on the interchange issue, our concern is that the master DVD
should be readable on all DVD-ROM drives. We use diagnostic software to
check all master CDs and plan to do the same with DVD. This in itself
is not a guarantee, but at least provides the peace of mind that each
disc has been written correctly and is readable on our equipment.
Analogue media will not last for ever and analogue playback equipment is
gradually being phased out. This is a reality and move to digital is
becoming inevitable. I think the biggest question for most archives is
when to make the move and, once that decision has been made, the next
question is how to make the most of the technology available at that
time within the limits of available funding. Granted, uncompressed
digital video technology is available, but who can afford it?
Wayne Williams
W. Williams
Project Manager, Digitising
International Library of African Music
Rhodes University
6140, Grahamstown
South Africa
TEL: +27 46-603 8547
FAX: +27 46-622 4411
DVDs/DVD-Rs are great for access and distribution but not for archiving
most
legacy archival material.
One archival issue with DVDs/DVD-Rs is that heavy compression is used
and
compression has two potential problems. One is the loss of the detailed
information like fluffy clouds, fine hair, grass, etc and archival
material
should never be degraded. The other potential problem with compression
is
whether or not compression artifacts will show up in the future when the
DVD
is copied to a newer format.
The second archival issue is how stable the medium is. At this time, I
trust
only Mitsui Gold.
The third archival issue is interchange. Will your DVD-Rs play on all
makes
of DVD players? Our evidence with CD-Rs is that the answer is no and
the
density of DVDs is much greater than CDs.
Jim Wheeler
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