Equipping a Video Digitisation System

Last updated: 27 January 2009
Published in: Digitising analogue media |
Tags: business & community engagement | digitisation | hardware | video |

Comments (0)

This document describes the configuration of a system which is intended to be used for the digitisation of analogue videotape to a computer hard drive. This document is intended to be of use to staff engaged in the digitisation of analogue video, whether dealing with only a few or a few hundred tapes.
The advice document Selecting a Video Digitisation System provides an overview of alternative types of equipment configurations.

Overview

This method of digitisation involves the use of a desktop computer-based system to convert an analogue video signal from a videotape into a digital one. The digital data is then stored on a computer hard drive as a digital video file. This is rapidly becoming the standard approach for the archival community as it can achieve the highest quality digital video files currently possible. Let's take a closer look at the key components required to build such a system:

Analogue playback device

The digitisation chain begins with the playback device. All analogue videotape formats (with the exception of VHS) are likely to now be unsupported by manufacturers. New players are typically unavailable but reconditioned players are often obtainable. Every year this situation worsens, leaving more and more videotapes unplayable. While this does justify the need for digitisation, it also presents something of a challenge when beginning to build a system. If possible, try to obtain a unit intended for professional rather than domestic use, this will help achieve optimum playback quality.

Image 1.1 VHS deck

Time base corrector (TBC)

A portion of an analogue videotape is devoted to controlling the rate of playback (25 frames per second in the UK). This area of the tape is susceptible to damage and deterioration, resulting in a poor quality, constantly ‘rolling' image. The video signal is sent from the analogue playback device to a time base corrector, which attempts to correct those errors and stabilise the image. The time base corrector typically required no user input, it simply sits in-line and a video signal passes through. A time base corrector is an inexpensive but extremely useful piece of equipment.

Image 1.2 Time base corrector or TBC

Colour corrector

While an in-line colour corrector is not a vital component of a digitisation system, it too is inexpensive and can prove very useful especially for older collections. The colour or ‘chroma' content of videotapes is also subject to unwanted change through deterioration. An in-line colour correcting unit can be used to adjust colour balance before digitisation.
There is a danger here, however that a subjective decision is made which does not reflect what the tape was supposed to look like (e.g. a scene may have been intentionally taped under coloured lights, this colour might later be mistakenly identified as a product of deterioration and removed via colour correcting). Some tapes have ‘colour bars' recorded at the beginning; these are intended for calibration purposes and give true representations of how colours are supposed to appear. If colour bars are present on tapes, the colours can be measured (using a software vectorscope program installed on the digitisation computer, for more information see Video Calibration) and corrections made with confidence. If colour bars are not present, standard test media (a tape which contains only an accurate recording of colour bars) can be played through the system and colour corrected for this.

Image 1.3 Colour corrector

Cube monitor

It is important to accurately monitor the video signal leaving the playback device and also the corresponding digital video signal after capture. A ‘cube monitor' is a production sector standard monitoring device which can represent colours extremely accurately. Typically it will have at least two channels and so can be switched between a signal coming directly from an analogue playback device to one coming from a computer.

Image 1.4 Cube monitor

Analogue to digital converter

An analogue to digital converter is at the heart of the digitisation system. It takes an analogue video signal (and its associated audio signal) and converts it into a digital equivalent which can be stored on a hard drive as a digital video file. A wide range of converters exist from inexpensive USB devices to external units intended for production use which cost many thousands of pounds and offer a choice of digital output formats. Typically, an internal analogue to digital converter or ‘capture card' will be used. Invariably this will be a PCI (Peripheral Component Interconnect) card which plugs into an expansion slot of a computer motherboard. It will provide input sockets to which the output of the analogue playback device (via any in-line signal processing units) can be connected. It will also have an analogue output connector which can be connected to a cube monitor in order to view the digitised video.
Key considerations when choosing a capture card are:
· Are the type of inputs compatible with the types of outputs your analogue playback device has? If not, an adaptor can sometimes be used, for more information see Interconnects and Signal Types).
· Does the capture card digitise video to a sufficient quality to meet your own quality assurance benchmarks? With several well supported and inexpensive capture cards now offering losslessly compressed or even uncompressed video digitisation, you can expect results of a very high standard.

Image 1.5 Analogue to digital converter

Desktop computer

Today's low cost desktop PCs can act as good base units which can be adapted for the task of digitising video by adding a small number of standard components. This can be done in-house if the required skills exist or can be undertaken pre-delivery by distributors or manufacturers such as Hewlett Packard or Macintosh. For video digitisation purposes little difference exists between Macintosh (‘Apple Mac') and Windows-based computers, although Apple Mac is likely to prove more expensive and may not be as supported by internal IT services. The Linux operating system too, is rapidly gaining in popularity. Ensure that the chosen operating system is compatible with any required software applications (for instance video editing programs).
Whichever operating system is selected, a system with sufficient specifications for comfortably handling high quality losslessly compressed video capture will typically start out with at least a 2.53GHz duel core processor, 2GB of RAM (Random Access Memory), an internal hard drive of 500 gigabytes, a standard video (display) card and internal soundcard, a DVD writer, a computer monitor, Wi-Fi, keyboard and mouse and pre-installed operating system.

Image 1.6 Desktop computer and TFT computer monitor

Additional computer requirements for video digitisation

Video capture card

It is extremely important to ensure, if intending to fit an internal video capture card in-house, that the expansion sockets on the computer's motherboard are free and are compatible. The capture card is likely to be a PCI card but several different types of PCI socket exist (e.g. PCI 2.2, PCI-X, PCI Express) and some are incompatible with others. The available range of capture cards is relatively small when compared to the available range of computer motherboards, therefore it is generally best to identify a suitable capture card for your project first and then source a computer which can accommodate it. Also, a specific capture card may have been designed to run under a specific operation system or even with a specific video editing application; this should also be checked before purchase.

External audio interface

While a cube monitor can be used for monitoring both image and sound, dedicated high quality and low cost USB devices are also popular for monitoring sound coming directly from the computer after or during digitisation. The output from these devices can be routed to either speakers or headphones. If the workspace has not been designed with the monitoring of sound in mind, quality headphones should be used.

Hard drive caddy

Hard drive technology is extremely versatile. Several drives (though usually not more than four) can be held within a single desktop machine, functioning either as separate drives or acting as a single drive in a RAID (Redundant Array of Independent Discs) configuration.
A hard drive caddy is a unit which removes the limit on the number of possible internal hard drives by making the swapping of hard drives quick and easy. Caddies allow hard drives to be used as removable storage media which can be safely stored away from the digitisation system. Both internal caddies (which fit into a computer's 5.25" bays) and external versions (which connect via a ‘FireWire' cable) are available.

 LTO Tape deck

A popular variation of this system is to replace computer hard drives as storage media with data tapes, such as an LTO (Linear Tape-Open). While LTO tapes do offer large capacity at costs similar to hard drives, stored files are not instantly available and must be copied back onto a hard drive before playback. Also, LTO decks which are used to read and write LTO data tapes are relatively expensive.

Stand-alone DVD-recorder

If efficiency in a primarily concern, it is possible to generate a DVD-video version of a videotape at the same time as the computer is capturing the analogue signal. This is achieved splitting the analogue signals (video & audio) before they reach the capture card input. The second set of outputs feed into a stand alone DVD-recorder. This unit is then set to ‘record' while the tape is playing back. Many stand-alone DVD-recorders now have a built in hard drive which allows a small amount of editing to take place before the DVD-video is actually created.

Software

In addition to the pre-installed operation system a number of special-purpose software applications are required for the digitisation of analogue videotape. A high quality video editing package such as Adobe Premier, Apple's Final Cut Pro or the open source application VirtualDub is used to interpret the data from the capture card, rename and save captured files. Applications such as these also provide the ability to trim clips, useful tools for monitoring the quality of the input signal (such as a software vectorscope) and transcoding tools to allow video files to be changed to other formats for delivery.
Your project may require some technical metadata which is best recorded during the digitisation process. Although all video editing packages have some ability to handle metadata, a relational database application is more commonly used.
Digital video files typically require a codec (compression/decompression algorithm) for playback. The codecs required for all types of video that your system is intended to handle should be installed onto the capture machine. For more information see File Types and Compression.
Many other software applications are likely to be required by a video digitisation project, depending on project aims; these might include checksum applications for detecting file errors, DVD-video authoring and burning applications and a selection of different video playback programs.

Image 1.7 Typical analogue videotape to hard drive equipment configuration (click for larger version)

Conclusion

Equipment required for the high quality digitisation of analogue videotape collections becomes more affordable everyday. In part this is due to the increasing capabilities of domestic components which can often be used instead of professional ‘production' equipment without loss of sound or image quality.
However, expensive production equivalents are seen as more robust and so may be desirable if a collection consists of more than a few hundred videotapes. Conversely, if a project is delivery (rather than preservation) focused, or is to deal with only a handful of videotapes in good condition, a ‘skeleton system' which excludes time base corrector, colour corrector and external audio interface may prove adequate. Suitable equipment should be identified and priced well in advance of the planned project start date and clearly associated with one or more stated project aims. This will help to justify any special funding required.

For all but the largest projects, capital equipment costs are likely to be tiny when compared to the labour costs involved. For this reason cost may be secondary to efficiency when choosing equipment.
JISC Digital Media offer a helpdesk service and offer advice on any aspect of the digitisation process, from clarifying equipment needs to delivery of a digitised video collection. 

Last updated: 27 January 2009
Published in: Digitising analogue media |
Tags: business & community engagement | digitisation | hardware | video |

Ask us a question

We provide a FREE enquiry service giving advice to the UK Further and Higher Education community.

You can ask us anything, typical questions include - "What formats should I use?" "How do I...?" "What tools can achieve the result I need?" "What is new and emerging?"

Ask now

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Comments (0)