As an extension of AVC, SVC provides the ability to adapt to heterogeneous environments. However, transcoding between SVC and AVC becomes necessary due to the existence of legacy AVC-based systems. This paper proposes a low-complexity SVC-to-AVC CGS transcoder in the pixel domain, which achieves approximately the same coding efficiency as the full re-encoding method. The output AVC bitstream modes are deduced by the proposed mode-mapping strategy. Different from previous works which simply use full search for SVC modes, the SVC modes are also examined and refined to generate suitable AVC modes in the proposed method. Simulation results show that proposed transcoder achieves 10 times speed-up with only 2% BDBR increase and 0.08 dB BDPSNR loss, compared with the full re-encoding method.