In this paper, a new dynamic bitstream switching method using progressive S-frames is presented. The progressive S-frames method can effectively switch two pre-encoded streams by reducing progressively the quantization mismatch. Progressive S-frames can provide better coding efficiency than an S-frame. Moreover, the proposed method can avoid the buffer overflow at the encoder and decoder sides while providing a soft transition between the quality levels of two bitstreams. The simulation results show that the proposed method is useful for the bit rate adaptation in heterogeneous networks.