A side information (SI) generation method is presented for the distributed video codecs with a scalable frame rate. SI interpolation, based on a hierarchical motion estimation with an adaptive block expansion, is proposed to reduce the power of the virtual channel noise, especially in sequences with lower frame rates. Blocks are classified into subframes in descending order of the estimated sum of the absolute difference (SAD), and each subframe is encoded if the maximum SAD of its blocks is larger than the estimated distortion of the key frames. Through a simulation, the proposed scheme is shown to achieve a coding efficiency close to that of H.264 with a zero motion even for very low frame rates.