Face object

is a special visual object defined in MPEG-4. Facial definition parameter(FDP) and facial animation parameter(FAP) are the sets of parameters to calibrate and animate the face object. The bitstream syntax for FDPs and FAPs in MPEG-4 are analyzed in this paper. The meaning of high level FAPs

viseme and expression

are explained with examples. All FAPs can be compressed with mask-based DPCM and/or DCT encoding. A rendering technology——displacement-controlling muscle model is proposed to reconstruct video sequences with natural facial expression from decoded FAPs and FDPs in MPEG-4 bitstream. There are two muscle models for different muscle stryles

parallel muscle and orbicular muscle. Different from traditional muscle models

which are controlled by intensity of muscle contraction

the proposed models are controlled by displacement of key-points affected by contraction of muscle. The reason behind this technology is that the visible displacement of key points is easier to be extracted from orighnal video sequence then the invisible muscle contraction. As an experiment result

reconstructed“Mona Lisa”with different expression is illustrated.