A mechanism for dynamically varying the frame rate of pre-encoded video clips is described. An off-line encoder creates a high quality bitstream encoded at 30 fps, as well as separate files containing motion vectors for the same clip at lower frame rates. An on-line encoder decodes the bitstream (if necessary) and re-encodes it at lower frame-rates in real-time using the pre-computed, stored motion information. Dynamic Frame Rate Control, used in conjunction with dynamic bit-rate control, allows clients to solve the rate mismatch between the bandwidth available to them and the bit-rate of the pre-encoded bitsream. It also provides a means for implementing Fast Forward control for video streaming without increasing bandwidth consumption.

In this demonstration session, we will demonstrate several examples of the state-of-the-art video compression standards MPEG-2, MPEG-4 and H.263. These demonstrations captured some of the recent work developed in the Digital Video Communications group at Sarnoff. For the MPEG-2 demonstration, the compression process uses standards compliant syntax with Sarnoff's proprietary algorithms to select the encoding parameters. For the MPEG-4 demonstration, we show the encoding results of the Verification Model including Sarnoff's contribution in scalable rate control and texture coding mode. In addition, we show the encoding results of a video streaming technology using H.263 and Sarnoff's proprietary technologies.

We analyze different retransmission (ARQ) schemes for error control in multicast protocols geared toward real-time, multimedia applications. We discuss why retransmission schemes are not inappropriate for such applications, but in fact can be quite effective. We present a quantitative analysis of such schemes, as well as simulation results, taking into account four different parameters (and not just the source throughput): (1) the probability of dropping a packet due to limited time for retransmissions; (2) the average time required to deliver a packet correctly to end receivers; (3) the number of times a packet will be retransmitted; and (4) the cost to the network, in terms of packet duplications, of retransmitting a packet. We reach the counter-intuitive conclusion that the optimum scheme, in terms of all four of the above parameters, in the most general scenarios (where several hosts with widely varying propagation delays and 'quality of connections' are participating in the session) is to immediately retransmit packets-preferably multicast-upon reception of a NACK from any receiver. We also demonstrate, again through quantitative analysis, the circumstances under which it would be beneficial (as well as those under which it would be counter-productive) to multicast control messages in the hope of suppressing duplicates and preventing the source from being overwhelmed by control messages.

An architecture and associated protocols are presented for managing multicast addresses and performing connection control for multicast communication applications. A scheme to partition the multicast address space on the basis of the network number is proposed (an underlying IP-based internetworking environment is assumed), and its performance and scaling characteristics are discussed. A protocol is then developed to provide for dynamic allocation and release of multicast addresses, as well as maintaining state information for a connection. The protocol is independent of the address partitioning scheme; it is also shown to be robust and efficient. Finally, we describe two different mechanisms that enable the use of a common port number by all session participants.

We describe a distributed architecture for managing multicast addresses in the global Internet. A multicast address space partitioning scheme is proposed, based on the unicast host address and a per-host address management entity. By noting that port numbers are an integral part of end-to-end multicast addressing we present a single, unified solution to the two problems of dynamic multicast address management and port resolution. We then present a framework for the evaluation of multicast address management schemes, and use it to compare our design with three approaches, as well as a random allocation strategy. The criteria used for the evaluation are blocking probability and consistency, address acquisition delay, the load on address management entities, robustness against failures, and processing and communications overhead. With the distributed scheme the probability of blocking for address acquisition is reduced by several orders of magnitude, to insignificant levels, while consistency is maintained. At the same time, the address acquisition delay is reduced to a minimum by serving the request within the host itself. It is also shown that the scheme generates much less control traffic, is more robust against failures, and puts much less load on address management entities as compared with the other three schemes. The random allocation strategy is shown to be attractive primarily due to its simplicity, although it does have several drawbacks stemming from its lack of consistency (addresses may be allocated more than once).>

We describe and evaluate the performance of the algorithms used in Columbia University's "Xphone" multimedia communication system. The system assumes a "best-effort" operating system and network, and provides synchronized video/audio acquisition/playback (locally or across a network) with minimized and bounded end-to-end delay. Synchronization is achieved using an algorithm based on time-stamps and device state information. The effects of jitter (delay variation) are mitigated using silence detection; the end-to-end delay is kept bounded using a restart mechanism. Finally, for live video sources, we describe a source bit-rate adaptation algorithm that maximizes the video image quality to the available network bandwidth and video display window size.

An improved algorithm for finding the translation parameters of the motion of rigid objects is presented. A critical analysis of the method of Tsai and Huang [IEEE Trans. PAMI-6, 1984, 13–26] to estimate the three-dimensional motion parameters of rigid objects showed that their method is extremely sensitive to noise, as conceded by the authors themselves. It was discovered that, in the presence of noise, the estimates for the rotation parameters were more accurate and consistent than those for the translation parameters. A modified program here combines the estimates for the less noise-sensitive rotation parameters with the basic motion equations in order to solve for the translation parameters. Simulations of the two methods were performed and it was observed that the modified algorithm improved the estimates for the translation parameters. In addition, a simple algorithm for the case where the motion is a pure translation is derived. Simulations again revealed that this simple algorithm is far less noise-sensitive than that of Tsai and Huang.