I. Introduction
Most of the Internet traffic today stems from user-generated videos on sharing web-sites and social networks. Video sequences pass through several stages of processing before they reach consumers, which often deteriorate visual quality. Moreover, the vast amount of user-generated video content and the increased diversity of end user devices (ranging from smaller and power-constrained mobile devices to large displays such as 4K Ultra HDTVs and TV walls) calls for a broad range of video quality to be supported. Adapting video quality to different use cases has become an important topic for researchers, content providers and distributors [1].