電機工程學系 ; We propose a two-pass R-D optimized quantization scheme for improving the coding performance of H.264 primary SP-frames under a given storage constraint on secondary SP-frames. The first-pass encoding of the proposed scheme collects the statistics required for fitting the model parameters which are used to characterize the bit-rates of secondary SP-frames and the distortion of primary SP-frames. As a result, in the second-pass encoding, these estimated model parameters are then used to obtain the optimal set of quantization parameters for all SP-frames of each GOP using the proposed R-D optimized quantization schemes. Experimental results show that our proposed schemes can improve coding performance of primary SP-frames under the given rate constraint.