Yutaka Ishibashi

A group synchronization mechanism for live media in multicast communications

To support multicast communications for live media, the authors propose a group synchronization mechanism and enhance an intra-stream/inter-stream synchronization mechanism which they previously proposed for live media. The proposed method employs estimates of network delays for adjustment of the output timing among the destinations. The authors have implemented the mechanisms on a lip-synch experimental system. Live video of a speaker and his voice captured at a source are multicast, and then they are synchronized and output at the destinations. This paper also presents the system performance such as coefficient of variation of output interval, total pause time, mean square error of synchronization, average output rate, and average delay.

A synchronization mechanism for continuous media in multimedia communications

This paper proposes a media synchronization mechanism which adjusts the output timing among stored continuous media streams in multimedia communications. The proposed method consists of intra-stream and inter-stream synchronization mechanisms. The inter-stream synchronization control is performed after the intra-stream synchronization control. Then, whether the intra-stream synchronization is still maintained or not is checked. The mechanism con be used in networks which have unknown delay bounds, and it does not suppose periodical generation of media units such as video frames. It also deals with two types of media streams depending on how strictly to synchronize media streams: tightly-coupled media streams and loosely-coupled media streams. Furthermore, we enhance the mechanism to support real-time-inputted media streams as in TV conferencing.

Mutually compensatory property of multimedia QoS

This paper studies user-level (or perceptual) QoS for multimedia applications over the Internet and demonstrates that media can compensate for each other from a perceptual point of view. For this study, we formulate the problem of the mutually compensatory property in terms of QoS mapping relation between application-level and user-level; we then conduct a simple experiment on lip synchronization to investigate the property. As a result, we observe the existence of the mutually compensatory property between voice and video. It is also shown that the property exists within a limited range of combinations of application-level QoS parameters. Furthermore, we point out the advantage of QoS control utilizing the property.

A group synchronization mechanism for stored media in multicast communications

This paper proposes a group synchronization mechanism, which synchronizes slave destinations with the master destination, for stored media in multicast communications. At the master and slave destinations, intra-stream and inter-stream synchronization mechanisms which were proposed by the authors are employed to output the master media stream and slave media streams synchronously. We achieve group synchronization by adjusting the output timing of the master media stream at each slave destination to that at the master destination. We also deal with traffic control by media scaling and control of joining an in-progress multicast group. Furthermore, the paper presents experimental results using an ATM network. It shows the validity of the mechanism and illustrates the influence of parameters on the system performance.

A comparative survey of synchronization algorithms for continuous media in network environments

This paper makes a survey of algorithms proposed for continuous media synchronization in network environments. We classify media synchronization control techniques used in the algorithms into four categories: basic control, preventive control, reactive control and common control. We also pick four representatives from among the media synchronization algorithms and give outlines of them in order to explain how the techniques are employed in each algorithm. Furthermore, we make a comparison among 38 algorithms in terms of factors such as clocks, advance information on network delay bounds and synchronization control techniques, which determine the design of each algorithm.

A Reservation Protocol for Satellite Packet Communication--A Performance Analysis and Stability Considerations

The dynamic behavior of a reservation system with a slotted ALOHA reservation channel is analyzed in this paper. It is assumed that each user handles one message at a time and that each message consists of a group of packets with a general probability distribution for group size. An approximate Markovian model of the system is developed on the assumption that the state transition can occur only at the beginning of each frame. The model is analyzed by an approximate analytical technique called equilibrium point analysis. The throughput and average message delay characteristics are obtained, and the system stability behavior is demonstrated. A procedure is also given to get the optimum set of system parameters under constraint that the system is stable.

Efficient Flexible Macroblock Ordering Technique

The H.264/AVC standard provides several new error-resilient features to enable the reliable transmission of compressed video signals over lossy packet networks. Flexible Macroblock Ordering (FMO) is one of the most interesting resilient features within the H.264/AVC standard. Unlike former standards, in which slices were constructed out of consecutive raster scan macroblocks, FMO suggests new slices composed of spatially distributed Macroblocks (MBs), and organized in a mixed-up fashion. H.264/AVC specifies seven types of FMO. The standard defines also an explicit FMO type (Type 6), which allows explicitly assignment of each MB within the frame to any available slice groups. Therefore new FMO types can be used and integrated into H264/AVC without violating the standard. In this paper we propose a new Explicit Chessboard-Wipe (ECW) Flexible Macroblocks Ordering (FMO) technique, which outperforms all other FMO types. The new ECW ordering results in effective error scattering which maximizes the number of correctly received macroblocks located around corrupted macroblocks, leading to better error concealment. Performance evaluations demonstrate that the proposed Explicit FMO approach outperforms all the FMO types. Both subjective and objective visual quality comparative study has been also carried out in order to validate the proposed approach.

Group synchronization control for haptic media in networked virtual environments

This paper proposes a group (or inter-destination) synchronization control scheme for haptic media in networked virtual environments where multiple users manipulate CG objects collaboratively in a 3-D virtual space by using force feedback devices. For group synchronization of haptic media, we enhance the synchronization maestro scheme, which the authors previously proposed for voice and video, so as to adjust the output timing of haptic media among the users. The paper demonstrates the effectiveness of the proposed scheme by experiment.

A comparison of media synchronization quality among reactive control schemes

This paper assesses the quality of media synchronization of recovery control schemes from asynchrony, which are referred to as reactive control schemes here, in terms of objective and subjective measures. We deal with four reactive control techniques: skipping, discarding, shortening and extension of output duration, and virtual time-contraction and time-expansion. We have carried out subjective and objective assessment of the media synchronization quality of nine schemes, which consist of combinations of the four techniques. The paper makes a comparison of media synchronization quality among the schemes. It also clarifies the relations between the two kinds of quality measures.

Live media synchronization quality of a retransmission-based error recovery scheme

This paper proposes a transport-layer error recovery scheme using retransmission for live audio-video streams transferred over QoS non-guaranteed networks. The scheme employs an enhanced version of the virtual-time rendering (VTR) media synchronization algorithm, which adjusts media rendering-time according to the network condition and is referred to as RVTR (retransmission with VTR). By an experiment, we assess the synchronization quality of both intra-stream and inter-stream in RVTR and four other schemes for audio-video transmission. A comparison of the experimental results indicates that joint application of retransmission control and the VTR synchronization control as in RVTR is effective in the improvement of media synchronization quality and that either control alone does not produce much improvement.