1:00, MMEDIA-P2.1
ADAPTIVE PLAYOUT SCHEDULING USING TIME-SCALE MODIFICATION IN PACKET VOICE COMMUNICATIONS
Y. LIANG, B. GIROD, N. FÄRBER
A new receiver-based playout scheduling scheme is proposed, which estimates the network delay from past statistics and adaptively adjusts the playout time of the voice packets. In contrast to previous work, the adjustment is not only performed in between talkspurts, but also within the talkspurts in a highly dynamic way. Proper reconstruction of continuous output speech is achieved by scaling individual voice packets using a time-scale modification technique which modifies the rate of playout while preserving voice pitch. Subjective listening tests show that this operation does not impair audio quality. Simulation results based on Internet measurement indicate that buffering delay and loss rate can be significantly reduced by adaptive scheduling.

1:00, MMEDIA-P2.2
KEY DISTRIBUTION FOR SECURE MULTIMEDIA MULTICASTS VIA DATA EMBEDDING
W. TRAPPE, J. SONG, R. POOVENDRAN, K. LIU
The problem of controlling access to multimedia multicasts requires the distribution and maintenance of keying information. The conventional approach to distributing keys is to use a channel independent of the multimedia content. We propose a second approach that involves the use of an data-dependent channel, and can be achieved for multimedia by using data embedding techniques. Using data embedding to convey rekeying messages can provide an additional layer of security when compared with the traditional approach. We then introduce multicast key distribution, and employ a recent tree-based key distribution scheme to exhibit the factors involved in transmitting keys using data embedding.

1:00, MMEDIA-P2.3
ERROR CONCEALMENT USING DATA HIDING
P. YIN, H. YU, B. LIU
Error concealment plays an important role in combating transmission errors. Methods of error concealment that produce better quality are generally of higher complexity, thus making some of the more sophisticated algorithms not suitable for real-time applications or are restricted to client devices with limited capability. In this paper, we propose an approach to use data hiding to facilitate the error concealment at the decoder. A set of features are extracted at the encoder and embedded imperceptibly into the host media. If some part of the media data is damaged during the transmission, the embedded features can be extracted and used for recovery of lost data. The use of data hiding leads to reduced complexity at the decoder. Simulation shows that our approach has better image quality than some well-known conventional error concealment methods.

1:00, MMEDIA-P2.4
ERROR-RESILIENCE IN MULTIMEDIA APPLICATIONS OVER AD-HOC NETWORKS
L. DOYLE, A. KOKARAM, D. O'MAHONY
Ad-hoc networking has been of increasing interest in recent years. It encapsulates the ultimate notion of ubiquitous communications with the absence of reliance on any existing network infrastructure. This paper presents a concept for robust operation of multimedia applications over such networks. Error resilient communication is achieved by using a new error detection and concealment technique that exploits information from the decoded image data itself as well as using information from the underlying network. This approach unifies information from both traditional Computer Science and Signal Processing domains. A layered architecture framework for the implementation of the proposed system is also described.

1:00, MMEDIA-P2.5
ADAPTIVE DELAY CONCEALMENT FOR INTERNET VOICE APPLICATIONS WITH PACKET-BASED TIME-SCALE MODIFICATION
F. LIU, J. KIM, C. KUO
For Internet audio applications, much effort has been involved in packet-level error control and delay jitter concealment. In this paper, a packet-based time-scale modification scheme for speech signal is applied to provide adaptive delay concealment at the receiver of an Internet voice session. The adaptive playout algorithm strives to minimize packet droppings for late-arrival packets and premature packets while keeping the end-to-end delay constrained. By stretching the voice segment up/down and incorporating the silence interval, the proposed algorithm could adapt quickly to accommodate fluctuating delays including delay spikes. The evaluation verifies the performance of the proposed adaptive playout, which improves the received speech intelligence under a tightly bounded average playout delay.

1:00, MMEDIA-P2.6
MAXIMIZING USER UTILITY IN VIDEO STREAMING APPLICATIONS
C. LUNA, A. KATSAGGELOS
In this paper, we study the design tradeoffs involved in video streaming in networks with QoS guarantees. We approach this problem by using a utility function to quantify the benefit a user derives from the received video sequence. This benefit is expressed as a function of the total distortion. In addition, we also consider the cost, in network resources, of a video streaming system. The goal of the network user is then to obtain the most benefit for the smallest cost. We formulate this utility maximization problem as a joint constrained optimization problem. The difference between the utility and the network cost is maximized subject to the constraint that the decoder buffer does not underflow. We present a deterministic dynamic programming approach to find the optimal tradeoff for both the Constant Bit Rate (CBR) and Renegotiated Constant Bit Rate (RCBR) service classes. Experimental results demonstrate the benefits and the performance of the proposed approach.

1:00, MMEDIA-P2.7
PASSIVE NETWORK TOMOGRAPHY USING EM ALGORITHMS
Y. TSANG, M. COATES, R. NOWAK
The paper presents a new method for characterizing communication network performance based solely on passive traffic monitoring at the network edge. More specifically, we devise a novel expectation-maximization (EM) algorithm to infer internal packet loss rates (at routers inside the network) using only observed end-to-end (source to receiver) loss rates. The major contributions of this paper are three-fold: we formulate a passive monitoring procedure for network loss inference based on end-to-end packet pair observations, we develop a statistical modeling and computation framework for inferring internal network loss characteristics, and we evaluate the performance with realistic network simulations.

1:00, MMEDIA-P2.8
A FEEDBACK SYSTEM FOR GRAPHICS VIDEO CODING AND NETWORKING
D. WANG, R. MERSEREAU
This paper presents feedback design of a desktop visual communications system. The system consists of video coding using a 3-D graphics model and video transmission over the Internet. To reduce the overall video quality degradation in visual communications caused by coding and networking errors, we jointly researched the compression and transmission of video signals. In building the 3-D graphics model-based coding structure, instead of using feedforward idea based on pixel intensity, we develop a three-level signal representation and an analysis-by-synthesis feedback framework. In prototyping the video over IP in desktop conferencing, we adapt the video encoders coding rates based on feedback of the network states and receivers. We contribute to the analysis, modeling, and transmission of multimedia signals for desktop visual communications.