This paper proposes a scheme of H.264 high-definition encoder/transcoder . The system is based on ASIC. Application-specific high-definition encoding/transcoding chip, software control module, HDMI interface, analog video/audio input interface and ASI input/output interface ,etc. are discussed in detail in this paper. The system also provides the Ethernet interface, which is used for real-time monitoring of coding/transcoding system . The proposed scheme with the property of good real-time and low cost accord with the need of high-definition digital TV front-end system.