New encoder library for Ogg Theora open source video codec
The Xiph.org Foundation's open source developers have released version 1.1 ("Thusnelda") of their reference implementation of the libtheora encoder library. Thusnelda is said to offer considerable quality and performance improvements over version 1.0.
Instead of completely rewriting Ogg Theora's royalty-free compression algorithm, Xiph.org is continuing the development of the "Truemotion VP3.2" codec released under an open source licence by On2 Technologies.
The new, backwards-compatible Thusnelda encoder is designed to allow Ogg Theora to achieve contemporary encoding efficiency. Thusnelda now uses rate-distortion optimisation (RDO), which leads to better quantisation decisions; in addition, adaptive quantisation causes better bit rate utilisation. The new version also offers faster and more detailed motion detection.
The same applies to its frequency space transform, which has been replaced with a better forward discrete Fourier transform (fDCT); for compatibility reasons, the previously used IDCT is still used for inverse transforms. New quantisation matrices are designed to cause fewer ringing and mosquito artefacts and to improve high contrast image quality, for example when overlaying text.
In addition, Thusnelda supports variable refresh rates and more colour subsampling variants (4:2:2 and 4:4:4). The developers also completely reworked its bit rate control, which now also offers 2-pass encoding. The library is available under a modified BSD licence.