Digitise videotape and audio tape: Parallels between audiovisual archiving and digital forensics in a world of format shifting.

by Andrew Martin

digitise videotape for legal and proof social proof.

As digital technology continues to influence our lives, it is important that we remain true to our past. As we digitise content from videotape, film and audio tape, and use digital tools to alter original video and audio records, we must make every effort to ensure that historical content retains its original integrity.

In our legal system, digital forensics relies on the veracity of audiovisual content as a form of legal proof. Equally important is the integrity of the video tape and audio tape content held in our archives, as this is historical proof. It can be difficult to predict what will become a valuable record, therefore, we must make every effort to secure as much historical audiovisual material in a digital form as we can. And in doing so, ensure it stays as true to its original state as possible.

When we compare digital forensics and audiovisual archiving it is evident (no pun intended) that these professions share important similarities in their management of video and audio content. Looking at videotape and audio tape digitisation and digital alteration practices for both forensic evidence and archival collections, you can see similar technologies employed and outcomes required. There are ethical and technological parallels between encoding, handling and processing. Authenticity, integrity and security of the content are underpinning principles in both fields.

Videotape and/or audio tape recordings used in court as forensic evidence must be admissible, requiring that:

1. provenance is known, recorded and verifiable; 

2. the content has not been altered or tampered with;  

3. if content is altered, it is fully documented and complies with the appropriate standards.

These same principles apply to audiovisual archives, as they are critical for understanding contextual information and ownership.


Best-practice audio digitisation

Technology obsolescence relating to videotape and audio is forcing content custodians, in this case archives and the legal fraternity, to format shift, primarily via digitisation. Digitisation of content on videotape or audio tape means that the content is no longer in its original form. It is easy to see how the authenticity, integrity and security of the content could be at risk from such a process, and needs to stand-up to scrutiny. For this reason, it is critically important that as organisations digitise videotape and audio, best-practice digitisation approaches are used to ensure that legal and social evidence is not jeopardised.

Analogue videotape or audio tape digitisation practices for preservation need to have the least possible amount of signal processing or alteration to ensure the integrity of the content. This same principle is required of material digitised for use in court proceedings. The practice provides assurances that the footage has not been tampered with during the digitisation process - this underpins authenticity.

To illustrate the best practice approach required, in 2014 DAMsmart was appointed to digitise a series of U-matic forensic videotapes for a high-profile trial. DAMsmart followed professional audiovisual digitisation standards to ensure the integrity of the content could not be challenged. The processes followed included:

> The tapes were handled prepared in line with best-practice standards.

> The digitisation workflow used enterprise grade transparent workflows to ensure no signal manipulation.

> All processes were logged and audible.

> The digitisation of the tapes took place in a secure and locked digitisation suite room.

> The digitisation took place under the watch of detectives to verify and monitor the process.

> DAMsmart was on standby to provide technical information of the digitisation process in court if required.

This robust process ensured that every effort was made to guarantee that this evidence was admissible in the court case. And while we may not always have police on hand, we do apply this same rigour to all videotape, film and audio tape archives we digitise.


The right tools for video digitisation

Digital enhancement and digital restoration are two practices that require the content to be altered.  In this process it is easy to see how authenticity can be contested. These processes can be in a legal context where evidence is modified for an outcome in a legal proceeding or in an archival context where an original piece of content is representative of time and place, and the effects of restoration could be considered to alter a social record.

Digital enhancement is an important tool in forensic analysis. Digital enhancement refers to the manipulation of the audio or video to draw attention to or away from a particular aspect of the signal. In effect, the process tries to create a clearer image or make sound more audible. Zoom, contrast, brightness adjustment and noise reduction are some features that may be required for enhancing the digital content. For example, enhancing an image of a blurry car. Or for use with facial and speech recognition technology, which is becoming very accurate and powerful even when applied to less than ideal recording environments.

Digital restoration on the other hand is used by archives to alter a piece of content to create a better end-user experience when the archival content is viewed or listened to, or restoring the content to its original intention. Digital restoration work may include processes such as dust and scratch removal, noise reduction, and dropout removal. For example, adjusting the tone in a colour grading process for film. As with digital enhancement, powerful algorithms are now available to automate some of these restoration tasks. In both cases, the following are guiding principles to assist in ensuring that the authenticity can be maintained:

> The process is undertaken using the appropriate professional software.
> Work is undertaken by a trained professional.
> The use of uncompressed or lossless compressed files with 10-bit depth and high chroma subsampling or up-converted to HD using motion compensated up-converters.
> All work is logged.
> An original copy of the unaltered audio or video file needs to be retained for preservation > purposes, or for future enhancement.

Both processes alter the original content and serve two different purposes, however, it is not always easy to tell them apart. To illustrate this, we recently provided services to the Melbourne University Archive. The audio tapes were an original field recording of Germaine Greer interviewing Federico Fellini in 1988. Fellini was off mic and the interview was in a crowded noisy area. DAMsmart used techniques to enhance Fellini’s voice using noise reduction, equalisation adjustment and voice enhancement. This would be closer aligned to enhancement as the audio was significantly altered, rather than restored to its original listening intention.

Audiovisual content plays a crucial role in our legal system and in our archives as an historical record. It is important that as digital technology continues to reshape our world, that the integrity of historical content on videotape and audio tape is upheld. It is important that the attributes of authenticity, integrity and security are always the primary consideration when you digitise videotape and audio tape records or alter digital content. If these tenants are compromised, the consequences for society could be devastating and widespread.