4. File Formats

Principles (slide 32)

In my opinion, the most valuable principle is: The archive must be able to work with the file formats that it holds. There are, of course, other very useful principles.

Different Purposes (slides 33–34)

There is no such a thing as a perfect file format that fits all needs in every situation. In the real world there are different file formats for different purposes:

  • The archive master should be at the highest quality that can be afforded over a long period of time – theoretically forever! If ever possible this should be an uncompressed format.
  • The archive should be able to provide to the professionals the formats that they need. Those formats are often called mezzanine.
  • Dissemination formats are also essential: they provide access and diffusion. As Elena Rossi-Snook said Archiving without access isn’t preservation, it’s hoarding.
Archive Master (slide 35)

There are two different routes for an image archive master:

  • Every single frame is stored as an single image file. This route is often used for cinema projection in movie theatres. The resolution is often 2K; the frames files grouped in one folder every film reel; and then there is the choice between linear or logarithmic encoding. Both solutions are approximately equivalent regarding the quality of the image. TIFF is generally easy to use on every modern computer, but needs 60% more storage space; DPX needs special software packages to be processed, but uses 37% less storage space.
  • All frames are stored together as a single file. This route is often used for professional television and video production. The resolution is often HD.

The IASA (International Association of Sound and Audiovisual Archives) recommendation for longterm digital preservation of sound has been adopted by EBU (European Broadcast Union) and ABU (Asia-Pacific Broadcasting Union).

The archive master’s formats are ideal also for digital restoration work.

Mezzanine (slide 36)

Apple ProRes 422 and Avid DNxHD 175x are both proprietary video formats, but those are today’s de facto industry standards. Therefore the archive must use them when working with professional postproduction facilities.

Dissemination (slide 37)

For access and diffusion there are many possibilities. We need a container that holds both the image and the sound, for example MP4, an open source solution.