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Subject: Longevity of digital videotape

Longevity of digital videotape

From: Mark Ritchie <avfilm>
Date: Wednesday, December 15, 1993
Kim Schroeder asked about the possibility of using D3 videotape for
archival purposes.  There are two factors to be examined when you are
considering digital videotape.

    1.  Physical durability of the tape. There is not much difference in
        the physical durability of the different digital videotapes, the
        advantage of the digital format is that it does not really
        matter.  If the tapes are stored in controlled conditions 50F
        30%RH they should easily last 25-30 years and then can be copied
        without loosing data. (assuming of course that you preserved a
        play-back machine).

    2.  Effects of compression algorithms.  D3 recording uses a video
        compression algorithm to store the data on the tape.  ALL
        existing compression algorithms are what is called "lossey" this
        means that they do not record all the data, some is "lost" by
        the algorithm.

There are two digital formats that do not use compression algorithms and
are thus "lossless", D1 and DCT.  I would recommend either of these.  In
addition these are "Component" video recorders.  This does not mean that
they come in separate boxes like your home stereo system but refers to
the manner in which the colour signal is encoded.  Component recording
is preferred because it allows for the correction of colour errors
caused during play-back by tape stretch, edge damage, etc.  The other
method is "Composite" recording where all the parts of the colour signal
are mixed together when recorded.

Mark Ritchie
Media Librarian
Audio-Visual Centre
University of Waterloo
Fax: 519-888-6197
"I was just out of college and still believed in
classifications and categories" -  Jean Renoir

                  Conservation DistList Instance 7:45
                Distributed: Thursday, December 16, 1993
                        Message Id: cdl-7-45-004
Received on Wednesday, 15 December, 1993

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