Adaptive video streaming is a key enabler for optimising the delivery of offline encoded video content. The research focus to date has been on optimisation, based solely on rate-quality curves. This paper adds an additional dimension, the energy expenditure, and explores construction of bitrate ladders based on decoding energy-quality curves rather than the conventional rate-quality curves. Pareto fronts are extracted from the rate-quality and energy-quality spaces to select optimal points. Bitrate ladders are constructed from these points using conventional rate-based rules together with a novel qualitybased approach. Evaluation on a subset of YouTube-UGC videos encoded with x. 265 shows that the energy-quality ladders reduce energy requirements by $28-31 \%$ on average at the cost of slightly higher bitrates. The results indicate that optimising based on energy-quality curves rather than rate-quality curves and using quality levels to create the rungs could potentially improve energy efficiency for a comparable quality of experience.

The environmental impact of video streaming services has been discussed as part of the strategies towards sustainable information and communication technologies. A first step towards that is the energy profiling and assessment of energy consumption of existing video technologies. This paper presents a comprehensive study of power measurement techniques for video encoding and decoding that is comparing the use of hardware and software power meters. An experimental methodology to ensure reliability of measurements is introduced. Key findings demonstrate the high correlation of hardware and software based energy measurements for the case of two video codecs across different spatial and temporal resolutions at a lower computational overhead.

As the impacts of climate change become evident worldwide, organisations across all sector of the economy are actively aiming at reducing their carbon footprints. Video streaming has been in the spotlight since the beginning of the pandemic. Previous work has identified opportunities to reduce electricity consumption, yet methods to reliably estimate the carbon reduction potential from interventions on video streaming systems are currently lacking. In particular, not enough consideration is given to the consistent methodological approach to impact assessment required to adequately account for the complex interactions between changes to a service and operational and structural effects at internet-scale systems at varying time scales. In this text, we review the state of knowledge and propose a consistent short-term marginal approach for the assessment of the short-term decarbonisation potential of interventions. We illustrate this with a simplified example intervention and contrast it to previous methodologically inconsistent approaches, in which we evaluate the temporary reduction of the video spatial resolution of user-generated content video on demand from 1080p to 720p in a fixed ladder scenario over one month in the UK. We find that the carbon reductions mainly come from savings at user devices, but are overall negligible at 0.5 gCO2e per day per typical laptop-viewer.

We present the DIMPACT /dimpækt/ tool for environmental assessments of digital services. The tool enables digital media providers to calculate energy consumption and associated environmental impact across the entire product system, including datacentres, networks and user devices. It is based on accepted standard methodologies and applies state-of-the-art research. The DIMPACT tool is used by major media organisations for environmental reporting and to support development of strategies to reduce environmental impact. It has significantly advanced the knowledge of carbon emissions of video streaming. The tool is part of the wider DIMPACT project of companies that collaborate to exchange knowledge, engage suppliers and expand the scope of the tool. In this text we provide an overview of workings of tool and its methodological foundation.

We present the EAM toolkit for life cycle modelling and impact analysis in environmental assessments. The open source toolkit was specifically designed to support maintainability and verification of models within integrated assessments, and has been used in research and industry. The tool offers features to support complex Life Cycle Assessment, including dynamic and scenario modelling, uncertainty and sensitivity analysis, a flexible domain specific modelling language and a visual editor. In this introduction we present the main features of the toolkit, summarise the high-level components and illustrate its use.

Recent research has advocated for a broader conception of evaluation for Sustainable HCI (SHCI), using interdisciplinary insights and methods. In this paper, we put this into practice to conduct an evaluation of Sustainable Interaction Design (SID) of digital services. We explore how SID can contribute to corporate greenhouse gas (GHG) reduction strategies. We show how a Digital Service Provider (DSP) might incorporate SID into their design process and quantitatively evaluate a specific SID intervention by combining user analytics data with environmental life cycle assessment. We illustrate this by considering YouTube. Replacing user analytics data with aggregate estimates from publicly available sources, we estimate emissions associated with the deployment of YouTube to be approximately 10MtCO2e p.a. We estimate emissions reductions enabled through the use of an SID intervention from prior literature to be approximately 300KtCO2e p.a., and demonstrate that this is significant when considered alongside other emissions reduction interventions used by DSPs.

Interactive devices and the services they support are reliant on the cloud and the digital infrastructure supporting it. The environmental impacts of this infrastructure are substantial and for particular services the infrastructure can account for up to 85% of the total impact. In this paper, we apply the principles of Sustainable Interaction Design to cloud services use of the digital infrastructure. We perform a critical analysis of current design practice with regard to interactive services, which we identify as the cornucopian paradigm. We show how user-centered design principles induce environmental impacts in different ways, and combine with technical and business drivers to drive growth of the infrastructure through a reinforcing feedback cycle. We then create a design rubric, substantially extending that of Blevis [6], to cover impacts of the digital infrastructure. In doing so, we engage in design criticism, identifying examples (both actual and potential) of good and bad practice. We then extend this rubric beyond an eco-efficiency paradigm to consider deeper and more radical perspectives on sustainability, and finish with future directions for exploration.

The use of information and communication technology and the web-based products it provides is responsible for significant emissions of greenhouse gases. In order to enable the reduction of emissions during the design of such products, it is necessary to estimate as accurately as possible their carbon impact over the entire product system. In this work we describe a new method which combines models of energy consumption during the use of digital media with models of the behavior of the audience. We apply this method to conduct an assessment of the annual carbon emissions for the product suite of a major international news organization. We then demonstrate its use for green design by evaluating the impacts of five different interventions on the product suite. We find that carbon footprint of the online newspaper amounts to approximately 7700 tCO2e per year, of which 75% are caused by the user devices. Among the evaluated scenarios a significant uptake of eReaders in favor of PCs has the greatest reduction potential. Our results also show that even a significant reduction of data volume on a web page would only result in small overall energy savings.