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Introduction

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Dirac is an experimental Open Source video codec, initially developed by BBC Research and Development. Its design is that of a conventional hybrid motion-compensated codec, except that the the function normally performed by a block transform in most MPEG standard and proprietary codecs is instead performed by the wavelet transform.

Dirac performs well in comparison with other codecs, and certainly much better than MPEG-2 (probably about twice as well). However, performance was not the only factor driving its design. Dirac is intended to be simple, powerful and modular, both conceptually and in implementation.The aim is to produce a codec which replaces the enormous variety of tools normally required for high-performance video compression with a much simpler design, with far fewer choices for the encoder to make. Ultimately, we want Dirac to develop into software that can be used for real-time encoding and decoding in image-processing applications: it is not supposed to be an algorithmic demonstrator. The software is a long way off this point at present, but with time we hope to get there.

We also want a wide variety of developers to be able to work with Dirac, and so we have tried to document Dirac as completely as possible. In addition to this algorithm document, we have provided doxygen-based comments on the reference code itself. We have produced a specification of the Dirac bit stream and decoding operations to allow others to develop compliant coders and decoders using as much or as little of the original Dirac software as they please. The high-speed Schrodinger implementation has been developed entirely from the specification.

If you want to use the Dirac reference code, you are referred to the README file in the distribution bundle for a description of what the various options mean.

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