Digital File Formats for Videotape Reformatting



Part 1. Detailed Matrix for Wrappers (unified table) ; Part 2. Detailed Matrix for Wrappers (multi-page) ; Part 3. Detailed Matrix for Encodings (unified large table) ; Part 4. Detailed Matrix for Encodings (multi-page) ; Part 5. Narrative and Summary Tables


The National Archives and Records Administration, with significant input from the Library of Congress, has compared video formats (generally older physical videotape material such as 1-inch, U-matic, VHS, and Betacam tapes) for reformatting and have developed four matrixes that offer comparisons of the wrappers AVI, MOV (QuickTime), Matroska, MXF, and MPEG-2 (ad hoc file wrapper), and the following encodings: uncompressed (various types), lossless JPEG 2000, ffv1, and MPEG-2 (encoding).


The narrative document accompanies the four matrixes and includes an explanation of the guiding principles behind their development, describes the character of the matrixes, goes into some detail about selected comparison factors (chroma subsampling, bits per sample and video range), clarifies some terminology used and provides four examples of how the matrixes are used to determine the correct format. Appendix A presents the summary versions of the matrixes and Appendix B provides some more technical information about chroma subsampling and video range.


Three principles guided the FADGI team that assembled this matrix: first, the importance of producing an authentic and complete copy of the original recording, as evidenced by the attention paid to multiple timecodes, captioning, and soundtracks. The second principle has to do with quality of reproduction. In general, the team preferred formats that maximized quality in both picture and audio reproduction. They favor uncompressed or losslessly compressed essences although given that some non-federal organizations with extensive broadcast holdings employ lossy compressed encodings for their archival master files (often called preservation masters), they have included one lossy encoding to stand for this class of formats in our comparison set. The third principle is the goal of producing archival masters that support the creation of access and access-support elements (such as closed captioning information).


There are two tables: one for wrappers and one for bitstream encodings. The centerpiece is a pair of matrixes that compare wrappers and encodings in terms of about forty factors and subfactors. These two extended matrixes are preceded by summary matrixes that highlight the key findings. The extended matrixes are followed by a discussion of the suitability of the formats for a number of illustrative video collection items. The matrixes presented here are neither comprehensive nor permanent. The list of available formats is certain to change over time, as will some of the assessments reported in the tables' individual cells.


This is an essential best practice document for archives planning the digitization of legacy videotape collections. It aids decision making while at the same time emphasizing the need to consider a variety of factors. The rationale behind the choices is clearly explained and it is not so technical that decision making is hindered. Archivists are urged to keep alert for updates as feedback from the field is incorporated into future editions. The set of documents could also be used by archives who have already digitized holdings, to review and check their own choices and to see if former business rules should be updated or amended.

Beth Delaney