Digitising for preservation

The decision was reached to tackle the deterioration of the video collection not only by caring for the physical carriers but also by digitising the entire content of the archive. We are creating new archival masters to ensure the continuation of content beyond the life of the fragile carrier. Unlike photography, few standards or precedents exist for generating new audio-visual archival masters. Following research carried out by Arts and Humanities Data Service (AHDS) Performing Arts, the PrestoSpace consortium, the Vienna Phonogrammarchiv and the International Association of Sound and Audiovisual Archives, we chose to store our data in uncompressed format, without the use of electronic compression algorithms which are often employed  to reduce the amount of data storage required. Storage of this uncompressed video data has advantages over compressed data:
  1. It is preferable for public exhibition and publication purposes, as publishers may wish to apply custom compression, dependent on delivery platform;
  2. Uncompressed data best meets the requirements of restoration and post-production;
  3. Existing procedures within the archival, museum and cultural heritage sectors prohibit the needless loss of information. Good practice involves pre-empting the application of similar measures to audio-visual and digital data.

For a discussion of the arguments for uncompressed storage, and an account of a process analogous to ours, see Franz Pavuza and Julia Ahamer's paper, "Linear Uncompressed Video Archiving on High-Performance Computer Tapes".

Our preservation process involves outputting analogue audio-visual data from contemporaneous U-Matic video players. This data is digitised via image stabilising hardware by two custom-built PC capture stations. The large size of this uncompressed video data necessitates the use of a low-cost yet well-trialled storage medium. Our primary storage medium is Linear Tape-Open (LTO) Ultrium, a format used heavily by the information technology community for reliable data storage. All data is error-checked and written to two separate LTO tapes which are held in geographically separate locations under a continuous cycle of error checking, refreshment and periodic migration. One set of data is held in the University of Bristol's Theatre Collection; a second identical security copy is deposited with AHDS.

In addition to this set of uncompressed archival masters, we identified the need for a second distinct digital data set of relatively low resolution content to serve as access copies; for this stage, see Preserving for access.