Changing video frame rate may require adding new frames. This can be done by interpolating the given frames over time. We describe a very fast algorithm for time interpolation of DCT encoded video. Given a sequence of DCT encoded frames, the algorithm produces the interpolated sequence of DCT encoded frames without computing DCT or inverse DCT. The idea is to exploit a simple shift property of DCT coefficients that holds for frame triplets. It is somewhat analogous to the shift property of Fourier coefficients that holds for frame pairs.