Most video platforms deliver HD video in high bitrate encoding. Modern video-conferencing systems are capable of handling HD streams, but using multiparty conferencing, average internet connections in the home are on their bandwidth limit. For properly managing the encoding bitrate in videoconferencing, we must know what is the minimum bitrate requirement to provide users an acceptable experience, and what is the bitrate level after which QoE saturates?. Most available subjective studies in this area used rather dated technologies. We report on a multiparty study on video quality with HD resolution. We tested different encoding bitrates (256kbs, 1024kbs and 4096kbs) and packet loss rates (0, 0.5%) in groups of 4 participants with a scenario based on the ITU building blocks task. We discuss the influence of group interaction and individual idiosyncrasies based on different mixed models, and look at covariates engagement and enjoyment as further explanatory factors. We found that 256kbs is still sufficient to provide a fair overall experience, but video quality is noticed to be poor. On the higher bitrate end, most people will not perceive the difference between 1024kbs and 4096kbs, considering in both cases the quality to be close to excellent. Independent on bitrate, packet loss has a small but significant impact, quantifiable in, on average, less than half a point difference on a 5-point ITU scale.

In modern video conferencing services, just as in commonvideo delivery, most of the resource optimization is taken careof in the codec layer. Modern codecs like H.264 use detailedperceptual models to optimize the data reduction in way that itis least noticed by us. Already early evaluations oftelecommunication systems could establish that there aredifferent thresholds for a good quality depending on thesituation. It is further known that subjective quality perceptionsvary from user to user. But the space of user and context factorsis still largely unexplored. To gain insight in which parametersare key in differentiating quality perception, we need to explorethe interaction in different situations while keeping a tightcontrol over the system parameters. In this paper we explorehow clustering participants by their interaction or ratingbehavior can reveal subgroups that show significantly differentperception of the QoE delivered by the same videoconferencingsystem. While for a cluster of users we find video quality toinfluence other QoE dimensions such as audio, for anothercluster this is not the case. We explore whether this effect is dueto conversational dynamics (contextual factor) or individualpreferences (user factor) and discuss what this would mean forthe design of future video-conferencing systems, that want todynamically adapt to situation and participants.