Tuesday, May 01, 2012

Preserving Moving Pictures and Sound.

Preserving Moving Pictures and Sound. Richard Wright. DPC Technology Watch Report 12-01. March 2012. [PDF]
This excellent report is for anyone with responsibility for collections of sound or moving image content and an interest in preservation of that content. For audiovisual materials, digitization is critical to the survival of the content because of the obsolescence of playback equipment and decay and damage of physical items, whether analogue or digital.

The basic technology issue for audio/visual content is to digitize all items on the shelves, either for preservation or access. The risk of loss is high. Another issue is moving content from the current media to digital files. A third issue is preserving the digital files. This report describes the techniques for preservation planning, digitization and digital preservation of audiovisual content, and describes the technologies.  Preservation of these materials is difficult because they are physically, culturally, and economically different.
Explanation of signals and carriers. "Digital technology produces recordings that are independent of carriers. Carrier independence is liberation". Digital preservation of the digitized signal means to preserve the numbers, but also the technology to decode the numbers. ‘Maximum integrity’ means keeping the full quality of the audio and video. As far as possible, the new preservation copy should be an exact replica of the original: the content should not be modified in any way’. This may be difficult to achieve.

The two basic kinds of preservation action are: 1) changing the audiovisual content within a collection, or normalization; 2) changing the system that holds the collection.
There are four main factors in an analogue or digital conservation program:
  1. packaging (wrappers), handling and storing;
  2.  environmental conditions;
  3.  protecting the masters; and
  4.  condition monitoring, maintaining quality.

The four PrestoPRIME requirements for effective access to time-based media are:
  1. granularity: division of the content into meaningful units;
  2. navigation: the ability to select and use just one unit,
  3. citation: the ability to cite a point on the time dimension of an audio or video file, with a permanent link
  4. annotation: the ability of a user of content to make time-based contributions
Other topics include access rights, implications for small collections or institutions. The digitization standards, encoding, wrapper and metadata are all agreed and well documented.  There is no reason for the basic encoding to ever be changed, though wrappers may eventually become obsolete. All archives need to be aware of the risk of loss of embedded metadata. Finally, surveys have shown that in universities there is a major problem of material that is scattered, unidentified, undocumented and not under any form of preservation plan.

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