Symmetric extension for nonexpansive multirate signal processing with M-channel maximally decimated filter banks are considered. Nonexpansive multirate signal processing is possible when the period length of the symmetrically extended signal is divisible by the downsampling ratio, M, of the multirate system. In some cases, symmetric extension will result in subband signals with different lengths for each subband. On the other hand, when the finite length signal whose period length after appropriate symmetric extension, does not equal an integer multiple of M, DC insertion symmetric extension method is proposed. With DC insertion symmetric extension, nonexpansive multirate signal processing is possible for finite length signals that cannot achieve nonexpansive multirate signal processing by conventional symmetric extension method.