The basic function of set-top box is to receive digital TV programs. The tuning module receives RF signals, down-converts them into IF signals, then converts them into digital signals, and then sends them to QAM demodulation module for demodulation, and outputs serial or parallel data of MPEG transport stream. The demultiplexing module receives the MPEG transport stream and extracts the PES data of the program, including video PES and audio PES.