Reducing Encoder Bit-Rate Variation in MPEG Video

Abstract

A shortcoming of current video transmission using the MPEG standard is that its encoder produces a variable bit rate (VBR). Due to this, the encoder output has to be buffered and released over the network at a constant rate. This buffering of the encoder output introduces an additional delay between the encoding and decoding phases of the video transmission. To remedy this problem, we present a strategy to distribute the load produced by the encoder as evenly as possible, i.e., try to have a constant bit rate (CBR). This is done by treating the slices in each frame separately while compressing them and then mixing the different kinds of slices that are sent over the network. The resulting load variation is much more uniform, reducing the buffering delay and making future bandwidth requirement estimates more accurate. Operations. Rajat Agarwal is now with Lucent Technologies. This paper is an extended version of a shorter paper presented at IEEE ICMCS 1999. mization of multimedia data transmission and retrieval techniques.Although there is an increasing number of academic and industrial projects [4-6] dealing with multimedia communication in wired and, more recently, wireless networks, many problems remain to be solved. This is especially true in real-time applications where a specified quality-of-service (QoS) for each individual connection, rather than the average QoS, must be guaranteed a priori. In real-time multimedia communication, the delay of each cell or packet, rather than the average delay, is the QoS. One approach towards this goal is to smooth the multimedia data such as video so that it can adapt to the bursty nature of network traffic [7,8]. In [9], a bandwidth smoothing technique is used across a sequence of nodes with buffers when a service provider has control over a subpath between the server and the client. Another approach is to tune the network and its communication protocols to better provide delay guarantees to variable-bit-rate multimedia traffic [10][11][12].Our objective here is to reduce the variation in the bit-rate produced by the encoder in MPEG (Motion Picture Experts Group) video. During transmission of Rajat Agarwal received the M.S. in Computer Science from the University of Houston. He is currently a Member of the Technical Staff at Lucent Technologies. His research interest is in real-time multimedia systems.

On the Error Resilience of Rate Smoothing using Explicit Slice-Based Mode Selection

“…A regular I slice update scheme is proposed by [2] to replace the structure of GOP, which efficiently decreases the video stream load variation. Similar approach is addressed in [3] for applications which transmit combinations of B and P slices. In [4] an encoder-based rate smoothing algorithm is developed for the low delay scenario.…”