Mahesh Balakrishnan

Variable-rate tree-structured vector quantizers

In general, growth algorithms for optimal tree-structured vector quantizers do not exist. In this paper we show that if the source satisfies certain conditions; namely, that of diminishing marginal returns; optimal growth algorithms do exist. We present such an algorithm and compare its performance with that of other tree growth algorithms. Even for sources that do not meet the necessary conditions for the growth algorithm to be optimal, such as for speech with unknown statistics, it is seen by simulation that the algorithm outperforms other known growth algorithms, For sources that do not satisfy the required conditions, the algorithm presented here can also be used to grow the initial tree for the pruning process. The performance of such pruned trees is superior to that of trees pruned from full trees of the same rate. >

Global optimization of multiplexed video encoders

An algorithm is presented for increasing the overall video quality of multiple variable rate video encoders multiplexed onto a single constant bit-rate channel. This enables an encoder, that is processing complex video, to use more of the channel bandwidth than an encoder that is compressing less complex video. The encoder rates are continually adapted. A rate controller determines the channel rate for each encoder as well as the target rate allocated to individual pictures encoded by the encoders. The target rates for individual pictures are computed in order to maintain constant quality across encoders while the encoder channel rates are derived so as to avoid encoder and decoder buffer underflow and overflow.

Buffer constraints in a variable-rate packetized video system

This paper provides an analysis of the buffers in a variable rate video encoding system and provides necessary conditions that need to be met by the channel and the encoder buffer control mechanism in order to ensure that the decoder and encoder buffers do not underflow or overflow. It is also shown that this can be achieved through the monitoring of just the encoder buffer. The paper also provides an algorithm that allows encoders to change their rate, by dynamically changing their logical buffer sizes, and lists the conditions that need to be met prior to the change in channel rate.

Extracting coding parameters from pre-coded MPEG-2 video

We investigate the problem of MPEG-2 video quality degradation due to re-encoding using different coding parameters. We examined the statistical properties of pre-coded video and discovered that the coding parameters can be recovered from pre-coded video because the compressed video is represented by a limited set of parameters. We present an algorithm to detect if a picture is intra-coded or original and extract coding parameters if the picture is intra-coded. We show with numerical results that the coding parameters can be effectively extracted from pre-coded video and used to reduce additional coding loss, thus greatly improving the performance of multiple-generation coding.

Digital video and the national information infrastructure

Abstract This paper gives an overview of the efforts in the United States to build high-speed networks for the delivery of digital video services to the homes of consumers. It details the obstacles that need to be overcome for digital video service to commence and the various network architectures and technologies that have been, and presently are being considered. The applications are described that will be enabled by such an infrastructure, termed the NII, as are two digital video services oriented market trials — one being conducted by a cable operator and the second by a telephone company.

Compressed video seamless switching using variable splicing parameters

We propose a new approach for creating splice points in compressed video streams. The resulting streams can be switched seamlessly, and therefore no decoder underflow or overflow events occur. The proposed variable splicing parameters (VSP) method eliminates major encoder buffer constraints and related video encoding issues associated with the standard approach for creating seamless splice points. These advantages are achieved at the expense of a minor increase in the splicing operation complexity. When using VSP splice points, the splicer has to wait a specific period of time (equal to the difference between the out point and in point decoding delays) before switching into the new stream (i.e. the stream with the in point).

Rate and buffer regulation in a video encoder for seamless splicing

An algorithm is presented for switching of compressed video streams in order to support the insertion of local programs and commercials for digital television production. This enables the creation of particular points in compressed video streams, whose characteristics allow to seamlessly switch between streams. These switching points are constructed by computing the buffer bounds in the video encoder so as to ensure that the decoder buffer does not underflow or overflow.