The advantage of degrading the QoS of a multimedia session is that it reduces the network bandwidth required for distributed multimedia applications, increasing the number of users that a multimedia server can support concurrently. Experimentation shows that users perceive a reduced frame rate for a continuous-media stream differently, depending on the content.

Video acceptability and frame rate

Real-time imaging has application in areas such as multimedia, virtual reality, medical imaging, and remote sensing and control. Recently, the imaging community has witnessed a tremendous growth in research and new ideas in these areas. To lend structure to this growth, we outline a classification scheme and provide an overview of current research in real-time imaging. For convenience, we have categorized references by research area and application.

Classification and overview of research in real-time imaging

Configurable parallel memory architecture for multimedia computers

This paper presents a video compression algorithm based on the adaptive wavelet packet decomposition and DPCM methods, in which, motion compensation is not used explicitly, but the effects of motion are accounted for through the low-high temporal subbanding and the DPCM procedure. The coefficients of high temporal subbands, initial lowpass subbands and the difference of low subbands from the DPCM loop are decomposed by adaptive wavelet packets based on a rate-distortion criterion, such that the subbands of the wavelet packets are efficiently quantized by a hybrid Scalar/Pyramidal Lattice Vector quantizer. We implement two versions of the proposed coding scheme based on a rate constraint and a quality (distortion) constraint. When the rate is constrained, all frames in a “group” are processed as a unit; our objective then is to minimize the overall distortion under the rate constraint specified for that group of frames. When quality constraint is imposed, pairs of frames are sequentially encoded; our goal in this case is to ensure that the distortion in each pair of frames remains below a prespecified value and to achieve this with a minimum bit rate used to represent that pair of frames. The results of the proposed algorithm compare favorably with those of 3D subband coding and traditional motion compensated video coding techniques. Although the encoding computational complexity of this scheme is higher than that of the existing 3D subband method, it is suitable for parallel implementation.

Video compression using adaptive wavelet packet and DPCM

The major drawback of the existing cluster placement scheme is the long response time caused by admission control if the number of clusters and the number of users are large. A circular skip-cluster placement scheme is proposed to reduce the size of the data buffer as well as the system response time. Furthermore, the popularity of each video is different in the real world. We propose a new popularity-based data allocation scheme to allocate data units within a cluster such that the corresponding data units of these popular videos are stored in those cylinders at one end of each cluster. Due to a higher spatial locality within these hot cylinders, some data units requested by the users are stored in the same cylinder such that one seek operation, one rotation, and one transfer operation are required to retrieve these data units. Therefore, the time required to retrieve data for these requests can be reduced, thus also reducing the system response time. Based on our results, the buffer size and the system response time can be reduced by half or more. These findings are essential for constructing video-on-demand systems that provide satisfactory performance.

A circular skip-cluster scheme to support video-on-demand services

We analyze the characteristics used to evaluate video coding algorithms and suggest rules for subjective quality evaluations.We examine video playback tasks and describe frame-differencing techniques for low-bandwidth systems.

A.A. Rodriguez

Papers

Evaluating Video Codecs