We propose a new context-adaptive arithmetic coding (CAAC) scheme for lossless bit rate reduction of parametric stereo (PS) in enhanced aacPlus. Based on the probability analysis of stereo parameters indexes in PS, we propose a stereo band-dependent CAAC scheme for PS. We also propose a new coding structure of the scheme which is simple but effective. The proposed scheme has normal and memory-reduced versions, which are superior to the original and conventional schemes and guarantees significant bit rate reduction of PS. The proposed scheme can be an alternative to the original PS coding scheme at low bit rate, where coding efficiency is very important.

We propose a new coding scheme for lossless bit rate reduction of the MPEG Surround module in unified speech and audio coding (USAC). The proposed scheme is based on context-adaptive arithmetic coding for efficient bit stream composition of spatial parameters. Experiments show that it achieves the significant lossless bit reduction of 9.93% to 12.14% for spatial parameters and 8.64% to 8.96% for the overall MPEG Surround bit streams compared to the original scheme. The proposed scheme, which is not currently included in USAC, can be used for the improved coding efficiency of MPEG Surround in USAC, where the saved bits can be utilized by the other modules in USAC.

As the number of different video compression algorithms in use and also the specific bit rates at which they are operated increase, there is a growing need for converters from one algorithm or bit rate to another. In general, this can only be accomplished by decoding and re-encoding. It has previously been assumed that the additional delays introduced by such decoding and re-encoding are additive and thereby become unacceptable for some interactive applications. This paper shows that it is possible to construct a transcoder such that the aggregate end-to-end delay is substantially less than the sum of the delays from the two encode and decode pairs. Two techniques are described. The first is more general while the second is simpler but is restricted to the case of reducing the bit rate and keeping the same compression algorithm. Results from simulations of the latter method are included.