Digital file formats

Overview

The pace at which the language and relevance of digital files evolves can be hard to keep up with. In an age where new developments also adds to the decline of previous iterations, knowing which file format and encoder are best suited for a project with specific technical, preservation and dissemination objectives can be rather complicated. This infokit aims to present an overview of the current state of play with regards to digital file formats for still images, audio and moving images, with one eye on the future. With such dynamic trends in how digital media is consumed, used and shared where there is currently uncertainty surrounding the take-up of formats in the wider field we have refrained from championing new, but untested formats. However, where communities are beginning to move away from previously popular formats we hope to reflect these shifts whilst remaining impartial. There is a bit of a catch-22 element inherent in adopting new but widely un-adopted formats, especially those with an open-source appeal. There are particular examples where, if taken up and widely implemented, some of these formats would benefit communities, and digital preservation. However, in order for these to become accepted standard they need to be widely supported by software communities and a great number of institutions need to adopt them. For this to happen involves an element of risk. Should you be an early adopter of a format that could fail to become embedded in standards or good practice? This is a question faced by a number of institutions at present and the only real correct answer to this at present is a fully informed one.

Choosing the right file format is intrinsic to the successful creation, digitising, delivering and preserving of digital media objects for a number of reasons. For example, the range of format properties we can choose from helps define the objective quality of a digital object. The dissemination of digital materials can be hindered by choosing poorly supported formats which can restrict or block viewing or playback. Furthermore, digital preservation can be hampered by selecting a proprietary format with a short shelf life, or a compressed format that irreversibly loses data. Overall, the process of selecting the right format for a project should not be taken lightly, and most projects will require the creation of files with the same content in multiple formats. For example a digital copy for sharing online needs to be in a different format to a copy saved as a preservation master. This infokit is designed not only to provide you with answers regarding which file format to use for which purpose, but provides file format suggestions for related purposes that may not have been initially considered.

In archival practice maintenance of digital media files is an ongoing process. We have already seen some early digital formats become obsolete, making them harder to playback than many ancient analogue recordings, and where certain file formats may be currently well supported, this may not always be the case. Although this infokit doesn’t focus solely on the issues of digital preservation a lot of the information provided is relevant.

 

Aims of this toolkit

• To provide a comprehensive understanding of what a file format is and what should be considered in choosing the correct format for your project
• To provide quick and practical answers to ‘what file format should I use for…? Covering common tasks and applications in education and heritage settings
• Offer help in identifying uncommon digital file formats
• To give in-depth technical information regarding the make-up of digital files, and file format properties.

For a collection of ‘best-fit’ recommendations for times when you need a simple solution to choosing a file format for a certain application. Based on common best practices these answers are only recommended as a guideline. If you require further advice related to your project aims please contact us.

 

Who is this toolkit for?

This infokit has not been compiled with one specific audience in mind due to the breadth of applications in which digital still image, audio and video files are used. However, in order to provide a useful resource to our key audiences we condensed information in order to address three key practices widely undertaken in education and cultural heritage; creation, digitisation andarchival activities and online delivery of digital media files.

As such this infokit should provide useful advice to those working in areas similar (although certainly not limited) to the following: digital media creators and sharers, managers of media collections or asset libraries, technologists involved in archival and digitisation work, managers of digitisation projects, curators of technical content, web publishers of digital media, learning technologists.

 

What is a digital file?

The format of a digital media file can be separated into the wrapper or container (the way the file is laid out) and the codec (the way the information is encoded: ‘codec’ is short for “compression-decompression algorithm”). We will refer to the components of a digital file in these terms throughout this infokit.