The ETNA Taxonomy

An overall aim of ETNA was to introduce new methods for establishing audiovisual quality requirements for a range of real-time multimedia applications. Until recently, there were few HCI-specific methods for assessing audio and video quality and the usability of videoconferencing systems. The taxonomy will address methods commonly used in the telecommunications industry, and explain why these are usually not suitable for assessing usability of audio and video. With the increasing popularity of networked multimedia applications such as media-on-demand and multimedia conferencing, application designers and service providers have to decide what level and type of audio and video should be provided. The awareness that such decisions have to be made with a view to user requirements and preferences has increased, but there is currently no well-founded methodology for determining what quality users both need and desire (see, for example: Rohaly et al., 2000; Libert et al., 2000). Methods currently used in the telecommunications and broadcasting industries are not suitable because they have a different aim in that they seek only to determine whether users can spot degradations in short audio or video clips (Watson & Sasse, 1998). These methods are not suitable for assessing usability of networked multimedia systems for several reasons: 2.1 Networked multimedia quality Networked multimedia quality is determined by a number of factors. Traditionally, assessment has focussed on the effect of different compression techniques and coding errors. With networked mul-timedia, the effects of delay and different levels of bandwidth have been investigated; delivery over the Internet adds the effects of packet loss and jitter; delivery over mobile systems means that connections may be interrupted or lost. Audio and video quality can also be affected by peripherals (such as microphones and speakers) and user operation of applications and peripherals. Finally, audio quality can influence the assessment of video quality, and vice versa. Indeed, within ETNA we found that quality decrements caused by such peripherals had a greater impact on users' quality perceptions than substantial changes in network performance (Watson & Sasse, 2000b). The taxonomy introduces a framework for audio and video quality assessment based on evaluation criteria (task performance, user satisfaction, and user cost), and explains how these criteria should be considered and balanced in any specific evaluation. In a work context, for instance, task performance is usually the most important consideration, whereas in a home entertainment situation, user satisfaction is the primary consideration. The first consideration of a …