Katherine S. Wang

A real time software-only H.261 codec

Video and audio conferencing over networks is becoming increasingly popular due to the availability of video and audio I/O as standard equipment on many computer systems. So far, many algorithms have concentrated on playback only capability. This generally results in unacceptable real-time performance with respect to latency and encoder complexity. We describe a software-only system that allows full duplex video communication. For our analysis and implementation we chose a DCT based method that uses motion estimation and is modelled on the CCITT H.261 standard. We discuss the algorithm, followed by an analysis of the computational requirements for each major block. The results presented show the effect of computational simplifications on signal to noise ratio and image quality. We also examine the processing needs for full resolution coding and project when this will become available.

Vector-quantization-based video codes for software-only playback on personal computers

This paper discusses a video compression and decompression method based on vector quantization (VQ) for use on general purpose computer systems without specialized hardware. After describing basic VQ coding, we survey common VQ variations and discuss their impediments in light of the target application. We discuss how the proposed video codec was designed to reduce computational complexity in every principal task of the video codec process. We propose a classified VQ scheme that satisfies the data rate, image quality, decoding speed, and encoding speed objectives for software-only video playback. The functional components of the proposed VQ method are covered in detail. The method employs a pseudo-YUV color space and criteria to detect temporal redundancy and low spatial frequency regions. A treestructured-codebook generation algorithm is proposed to reduce encoding execution time while preserving image quality. Two separate vector codebooks, each generated with the treestructured search, are employed for detail and low spatial frequency blocks. Codebook updating and sharing are proposed to further improve encoder speed and compression.

High-performance video codec for CD-ROM-based video playback

This paper discusses video compression and decompression strategies for use on general purpose computer systems where no specialized hardware is available. We first examine the alternatives and describe the performance and limitations of the first generation of such methods. A brief description is given of the possible algorithmic approaches. We introduce requirements for the encoder/decoder, and show that a vector quantization based scheme with image preprocessing and classification can provide the required performance. The remainder of the paper deals with the algorithm design and the tradeoffs made to meet the goals of realtime decode capability, compression ratio and image quality. Finally, we present results for the optimized algorithm and indicate areas which appear to be most promising for further work.

Performance of real-time software-only H.261 codec on the Power Macintosh

The widespread use of teleconferencing as a major role of remote communication has until now been stymied by the costs associated with deploying specialized hardware required to achieve good performance. Another constraint has been the incompatibility among the various systems that are available. These facts coupled with the rapid increase in computational power available on desktop systems convinced us of the value of a standards-based software solution. Leveraging the performance of the PowerPC RISC processors, we have implemented a software-only realization of the CCITT H.261 video coding standard. In this paper, we will discuss the performance of the software codec which has been optimized for the Power Macintosh 8100. Over ISDN and loaded Ethernet, the codec provides good visual quality in terms of spatial quality and frame rate over a range of bit rates (less than 64 to 384 Kbits/s). We will outline the structure of the software codec and discuss its performance.