In this thesis, DCT domain video compositing with embedded zerotree coding for multi-point video conferencing is considered. In a typical video compositing system, video sequences coming from different sources are composited into one video stream and sent using a single channel to the receiver points. There are mainly three stages of video compositing: decoding of incoming video streams, decimation of video frames, andencoding of the composited video. Conventional spatial domain video compositing requires transformations between the DCT and the spatial domains increasing the complexity of computations. The advantage of the DCT domain video compositing is that the decoding, decimation and encoding remain fully in the DCT domain resulting in faster processing time and better quality of the composited videos. The composited videos are encoded via a DCT based embedded zerotree coder which was originally developed for wavelet coding. An adaptive arithmetic coder is used to encode the symbols obtained from the DCT based zerotree codingresulting in embedded bit stream. By using the embedded zerotree coder the quality of the composited videos is improved when compared to a conventional encoder. An advanced versionof zerotree coder is also used to increase the performance of the compositing system. Another improvement is due to the use of local cosine transform to decrease the blocking effect at low bit rates. We also apply the proposed DCT decimation/interpolation for single stream video coding achieving better quality than regular encoding process at low bit rates. The bit rate control problem is easily solved by taking the advantage the embedded property of zerotree coding since the coding control parameter is the bit rate itself. We also achieve the optimum bit rate allocation among the composited frames in a GOP without using subframe layer bit rate allocation, since zerotree coding uses successive approximation quantization allowing DCT coefficients to be encoded in descending significance order
