2 research outputs found
The Big Picture on Small Screens Delivering Acceptable Video Quality in Mobile TV
Mobile TV viewers can change the viewing distance and (on some devices) scale the picture to their preferred viewing ratio, trading off size for angular resolution. We investigated optimal trade-offs between size and resolution through a series of studies. Participants selected their preferred size and rated the acceptability of the visual experience on a 200ppi device at a 4: 3 aspect ratio. They preferred viewing ratios similar to living room TV setups regardless of the much lower resolution: at a minimum 14 pixels per degree. While traveling on trains people required videos with a height larger than 35mm
Quality of experience in digital mobile multimedia services
People like to consume multimedia content on mobile devices. Mobile networks can deliver mobile TV
services but they require large infrastructural investments and their operators need to make trade-offs to
design worthwhile experiences. The approximation of how users experience networked services has
shifted from the inadequate packet level Quality of Service (QoS) to the user perceived Quality of
Experience (QoE) that includes content, user context and their expectations. However, QoE is lacking
concrete operationalizations for the visual experience of content on small, sub-TV resolution screens
displaying transcoded TV content at low bitrates.
The contribution of my thesis includes both substantive and methodological results on which factors
contribute to the QoE in mobile multimedia services and how. I utilised a mix of methods in both lab and
field settings to assess the visual experience of multimedia content on mobile devices. This included
qualitative elicitation techniques such as 14 focus groups and 75 hours of debrief interviews in six
experimental studies. 343 participants watched 140 hours of realistic TV content and provided feedback
through quantitative measures such as acceptability, preferences and eye-tracking.
My substantive findings on the effects of size, resolution, text quality and shot types can improve
multimedia models. My substantive findings show that people want to watch mobile TV at a relative size
(at least 4cm of screen height) similar to living room TV setups. In order to achieve these sizes at 35cm
viewing distance users require at least QCIF resolution and are willing to scale it to a much lower angular
resolution (12ppd) then what video quality research has found to be the best visual quality (35ppd). My
methodological findings suggest that future multimedia QoE research should use a mixed methods
approach including qualitative feedback and viewing ratios akin to living room setups to meet QoE’s
ambitious scope