MPEG-4 AVC encoded video streams have been analyzed using video traces and statistical features have been extracted, in the context of supporting efficient deployment of networked and multimedia services. The statistical features include the number of scenes composing the video and the sizes of different types of frames, within the overall trace and each scene. Statistical processing has been performed upon the traces and subsequent fitting upon statistical distributions (Pareto and lognormal). Through the construction of a synthetic trace, based upon this analysis, our selections of statistical distribution have been verified. In addition, different types of content, in terms of level of activity (quantified as different scene change ratio) have been considered. Through modelling and fitting, the stability of the main statistical parameters has been verified as well as observations on the dependence of these parameters upon the video activity level.
MPEG-4 High-Efficiency Advanced Audio Coding (HE-AAC) is designed for low bit rate applications, such as audio streaming in mobile communications. The HE-AAC audio codec offers a better coding efficiency since variable-length codes (VLCs) are adopted. However, HE-AAC has originally been designed for storage and error-free transmission conditions. For the transmission over bit error-prone channels, error propagation is a serious problem for the VLCs. Therefore, a robust HE-AAC decoder is desired, especially for mobile communications. In contrast to traditional hard-decision decoding, utilizing bit-wise channel reliability information, softdecision (SD) decoding has been known to offer better audio quality. In HE-AAC, the global gain parameter is coded with fixedlength codes (FLCs), while the scale factors and quantized spectral coefficients are coded with VLCs. In this work, we apply FL/SD decoding to the global gain parameter, VL/SD decoding to the parameters scale factors and quantized spectral coefficients. Especially, in order to apply VL/SD decoding to the quantized spectral coefficients, a new modified trellis representation in VL/SD decoding is proposed. An improved HE-AAC performance is clearly observed, with the support of both instrumental measurements and a subjective listening test.
