Abstract:MPEG-2 and MPEG-4 are two most popular international video compression standards.They will coexist in different systems and networks for a long time.For compatibility of these two video standards

this paper put forward three transcoding algorithms on the basis of detailed analysis of computational complexity.In the paper

the principle and implementation of two efficient transcoding algorithms are emphasized.Both of them are compromise between the computational complexity and reconstructed video quality.One is motion-information reusing algorithm

which meets the highest video quality requirement of studio.The other is real-time low complexity transcoding algorithm

which applies to lowest delay requirement of the network server and user terminal with limited computational performance.The simulation results of many test sequences testified the excellent performance of the algorithms.