Streaming video over the Internet requires mechanisms that limit the streams' bandwidth consumption within its fair share. TCP streaming guarantees this and provides lossless streaming as a side-effect. Adaptation by packet drop does not occur in the network, and excessive startup latency and stalling must be prevented by adapting the bandwidth consumption of the video itself. However, when the adaptation is performed during an ongoing session, it may influence the perceived quality of the entire video and result in improved or reduced visual quality of experience. We have investigated visual artifacts that are caused by adaptive layer switching -- we call them flicker effects -- and present our results for handheld devices in this paper. We considered three types of flicker, namely noise, blur and motion flicker. The perceptual impact of flicker is explored through subjective assessments. We vary both the intensity of quality changes (amplitude) and the number of quality changes per second (frequency). Users' ability to detect and their acceptance of variations in the amplitudes and frequencies of the quality changes are explored across four content types. Our results indicate that multiple factors influence the acceptance of different quality variations. Amplitude plays the dominant role in delivering satisfactory video quality, while frequency can also be adjusted to relieve the annoyance of flicker artifacts.

Subjective quality perception studies with human observers are essential for multimedia system design. Such studies are known to be expensive and difficult to administer. They require time, a detailed knowledge of experimental designs and a level of control which can often only be achieved in a laboratory setting. Hence, only very few researchers consider running subjective studies at all.

Abstract—Multi-dimensional video scalability as defined in H.264/SVC is a promising concept to efficiently adapt encoded streams to individual device capabilities and network conditions. However, we still lack a thorough understanding of how to automate scaling procedure in order to achieve an optimal quality of experience (QoE) for end uses. In this paper we present and discuss the results of a subjective quality assessment we performed on mobile devices to investigate the effects of multi-dimensional scalability on human quality perception. Our study reveals that QoE degrades nonmonotonically with bitrate and that scaling order preferences are content-dependent. We confirm previous studies which found common objective metrics to fail for scalable content, but we also show that even scalability-aware models perform poor. Our results are supposed to help improving the design of quality metrics and adaptive network services for scalable streaming applications. I.

There is an increasing trend to include streamed video data in 3D environments. Such environments allow potentially several concurrently visible videos on a single display device, and consequently, network and processing bottlenecks. As a first step towards an avoidance of such problems, we have performed subjective assessments using a 3D application prototype to determine how positioning of video in the 3D environment influences the user perception of reduced-quality videos. Using video clips from several genres, we have compared the influence of various ways to reduce video quality and users' perception of degraded quality. We evaluated the influence of distance and angle of the placement.

Scalable video is an attractive option for adapting the bandwidth consumption of streaming video to the available bandwidth. Fine-grained scalability can adapt most closely to the available bandwidth, but this comes at the cost of a high compression penalty. In the context of VoD streaming to mobile end systems, we have therefore explored whether a similar adaptation to the available bandwidth can be achieved by performing layer switching in coarse-grained scalable videos. In this approach, enhancement layers of a video stream are switched on and off to achieve any desired longer-term bandwidth. We performed user studies to evaluate the idea, and came to the far-from-obvious conclusion that layer switching is viable way for bit-rate savings and fine-grained bit-rate adaptation even for rather short times between layer switches.

In this paper, we propose a scalable video coding scheme for H.264/AVC video that fully utilizes the benefits of Switching frames (SP/SI) to facilitate user-friendly remote multimedia stream browsing and editing. A content aware rate-control algorithm is developed to adoptively determine the optimal encoding configuration for balancing the trade-off between video coding efficiency and temporal scalability. Our temporal scalable coding scheme is useful for implementing DVCR-like interactive functionality such as fast-forwarding and reversing in multimedia streaming applications such as Video-On-Demand, video broadcasting and remote video editing.

With the growing popularity of variable network technologies, it is highly desirable to enable effective and quick browsing of remote multimedia content. In this paper we present a method for quick access of remote video content as an initial step towards a full digital Video Cassette Recording functionality in multimedia streaming applications such as Video-On-Demand, video broadcasting and remote video editing.We propose a transcoding scheme for H.264/AVC video that fully utilizes the benefits of recently proposed SP- and SI-frames to facilitate user-friendly remote stream browsing and editing. The transcoding parameters can be adaptively changed and optimized to support different characteristics of H.264 video streams.