Research Of Source Coding In Multimedia Communications Systems

Multimedia communications are the intergration of multimedia technology and communications technology . It syncretizes the interactive of computer and the distributed of communications and the realization of Multimedia . Multimedia communications have some prooerties , such as many kinds of information , huge data and height real time demand . The key technology of multimedia source coding is digital compress coding .The paper falls into two main parts : digital speech compress coding and moving picture compress coding . Researching the digital speech compress coding , the fundamental technology of speech compress coding are introduced which include PCM , ADPCM , ADM , SBC of wave coding , channel vocoder , formant vocoder and LPC of voice coding .Two kinds of vocoder , Regular Pulse Excitation / Long Term Prediction (RPE/LIP ) and Vector Sum Excitation Linear Prediction (VSELP) , which are using in mobile communications systems in Europe and America , as examples , are explained to study specific speech coding algorithm . First , testify why RPE/LIP uses regular pulse excitation . Then some main coding processes , such as pre-processing , LP analysis , short term analysis , long term prediction and Pulse Excitation coding are studied . Researching VSELP , we pay attention to its codebook structure and search .Last, G.729A is studied in detail, which is a representation of 3G speechcoding . In this part, first, the principle of G.729A encoder and decoder are introduced . Then the whole process of G.729A , includes pre-processing , LP analysis , open loop pitch analysis , adaptive codebook search , fixed codebook search , quantization of the gains , memory update , parameter decoding procedure and post processing . Explain fully the purpose , input and output of every process . Third , implement the encoder and decoder with Visual C++6.0 , and test their speed , and also test their speech quality in differ BER by comparing the wave of speech , analysising spectrum and using subjective testing . The test results show that the encoder and decoder are fit for practical applications . Last make a real time record compress and play decompress speech software by using the G.729A encoder and decoder .In the research of moving picture compress coding . First , study the digitalization , inner frame transform compress coding , moving predict compensation between frames and video structure , base on three international standards : H.261 ^ H.263 and MPEG . For MPEG-2 and MPEG-4 , emphasize on their profile , level , scalable and decoder process , such as variable length decoding , inverse scan , inverse quantization , inverse DCT and motion compensation . Last argument for the bit stream conversion between MPEG-2 and MPEG-4 is studied.