The enhancement layer rate allocation problem is examined in progressive fine granular scalable (PFGS) video coding.The problem arises from the fact that different frames in the enhancement layer have different rates in PFGS coding.A rate-distortion (R-D) function for a multi-frame group is first established for enhancement layer PFGS coding

followed by experiments to verify its validity using real test sequences.Optimal rate allocation among frames in the group is then given based on the R-D function

together with a simple implementation that is suitable for applications like streaming video.Experiments show that

compared with uniform bit allocation

optimal bit allocation not only makes the quality variation in decoded video much smoother

but also improves the average PSNR of PFGS coding by 0.3~0.5dB.