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Software-only video codecs can provide good playback performance in desktop computers with a 486 or 68040 CPU running at 33 MHz without special hardware assistance. Typically, playback of compressed video can be categorized into three tasks: the actual decoding of the video stream, color conversion, and the transfer ofdecoded video data from system RAM to video RAM. By current standards, good playback performance is the decoding and display of video sireams of 320 by 240 (orlarger) compressed frames at 15 (or greater) frames-per-second. Software-only video codecs have evolved by modifying and tailoring existing compression methodologies to suit video playback in desktop computers. In this paper we examine the characteristics used to evaluate software-only video codec algorithms, namely: image fidelity (i.e., image quality), bandwidth (i.e., compression), ease-ofdecoding (i.e., playback performance), memory consumption, compression to decompression asymmetry, scalability, and delay. We discuss the tradeoffs among these variables and the compromises that can be made to achieve low numerical complexity for software-only playback. Frame-thiferencing approaches are described since software-only video codecs typically employ them to enhance playback performance. To complement other papers that appear in this session of the Proceedings, we review methods derived from binarypattern image coding since these methods are amenable for software-only playback. In particular, we inroduce a novel approach called pixel distribution image coding. L INTRODUCTIONDigital video in desktop computers currently consists of two categories of video codecs (compressor/decompressors). The first category consists of video coding algorithms that exhibit low complexity for playback and therefore produce compressed video streams that can be decoded and displayed in desktop computers without special hardware assistance -the compute?s CPU performs all of the decompression and display tasks. This set of video codec algorithms is typically referred to as algorithms amenable for software-only video playback, or software-only video codecs. The side effect of low playback complexity algorithms is that they tend to exhibit limited image quality. The second category of video codecs in desktop computers is typically referred to as hardware-assisted video codecs. Like the video coding algorithm described by the Moving Pictures Expert Group (MPEG) [1], hardware-assisted codecs are capable of providing a substantial increase in image quality in comparison to software-only video codecs. Figure 1 depicts the image quality versus playback complexity space spanned by the two sets of video codecs. Notice that software-only video codecs are within incremental quality of each other. An imaginary horizontal line above the domain spanned by the software-only video codecs reminisces the limited quality they provide. Likewise, an imaginary vertical line to the left of the domain of hardware-assisted codecs, indicates that these algorithms are too complex for software-o...

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