Evaluating preservation strategies for audio and video files Presentation for the DELOS Workshop By Franz Pavuza Mai 2005, Heraklion, Greece Phonogrammarchiv, Austria

2 Audio and Video Files Source: VUT Homogenuous collection Few file formats Software migration often combined with hardware migration Very large collections

3 Evaluating preservation strategies Introduction Adapted Utility Analysis Set objectives Evaluate alternatives Define preferences and decide Summary Source: VUT

4 Utility Analysis Developed in the 1970s Applied mainly for infrastructure projects, such as dams, bridges, neighbourhoods Well expandable Adapted to fit the preservation requirements Source: VUT

5 Utility Analysis procedure Define project objectives Assign effects to the objectives Define alternatives Measure alternatives performance Transform measured values Weight the objectives Aggregate partial and total values Rank the alternatives Source: VUT, Hanusch et. alt.

6 Define project objectives Two workshops to identify requirements 324 criteria identified Composition of tree depends on collection specific requirements Source: VUT

7 Assign effects to objectives Objective i Measurable effects: for example in frames per second, EURO per year, Megabyte, …… Subjective evaluation: Valued with subjective impression, necessary, where no measureable evaluation found, for example usability (example: time to understand the system,..) or watermarking. An extreme form is a simple yes/no decision. Source: VUT

8 Definition of alternatives Migration & Standardisation Emulation & Encapsulation Computer Museum Digital Tablet No change to the strategy No preservation effort Migrate documents to U-Matic MPEG DPS Std.DV ….. Encapsulate digital objects Try to construct a digital tablet Try to preserve the hardware environment Do not adapt the strategy Do not take care of preservation Source: VUT

9 Alternatives‘ evaluation Measure of the alternatives‘ performance, using either: Original files Files from a testbed Source: VUT Std. DV Digi- Beta PAL- VHSSVHSU-Matic Beta CamMPEG NTSC- VHSDPSHi8 Signal representation (e.g. RGB,..) Replay variance Picture-audio synchronisation Stereo

10 Transform measured values 54321N.A Replay variance Picture-audio synchronisation Frame rate>80fps80-50fps50-30fps30-20fps20-10fps< 10fps Transform the results to make them comparable PAL-VHSSVHSU-MaticHi8 Replay variance3454 Picture-audio synchronisation5543 Frame rate5555 Define the transformation table: Source: VUT

11 Weighting Appearance Structure Behaviour 50% 25% 45% Final weight of all leafs: 10% 25% Appearance0,5 * 0,45 = 0,225 Structure0,5 * 0,45 = 0,225 Behaviour0,5 * 0,10 = 0,05 Σ(leaf weights) = 1 Σ(w 1,j ) = 1 Source: VUT

12 Aggregating part values leaf weights x transformed values sum of all part values of a strategy includes also „not acceptable“ alternatives Part values per objective Total value per alternative Source: VUT

13 Results Source: VUT DPS 3,17 Std. DV3,16 Beta Cam3,16 Digi-Beta3,15 NTSC-VHS3,14 SVHS3,10 MPEG3,10 U-Matic3,09 PAL-VHS3,05 Hi82,98 Minimal difference in measurement Process characteristics & costs are almost identically Significant difference in file characteristics Best solution (DPS) reaches 63% of an optimal solution

14 Summary Composition of objective trees depend strongly on the collection‘s requirements Different solutions vary mainly in the objective tree composition and the objective‘s weights „standard“ objective trees evolve for specific scenarios We now have: A powerful tool to make accountable preservation decisions Detailed objective tree for audio / video preservation Decision process is transparent Source: VUT