Why we RVLCs usually applied only to motion vectors If you wanted to reducethe bitrate impactwhat changes would you make?

Answer 1

VLC table is to increase error resilience. In particular, if one separates the motion vectors from the DCT coefficients and apply horizontal prediction, one can increase error resilience by using backwards decodable VLCs also known as Reversible Variable length coding (RVLCs). This data partitioning is not going to happen in H.263+, but is likely to be an option in H.263++. It is therefore desirable to try to construct the new VLC table as a RVLC table. Thus, we RVLCs usually applied only to motion vectors. If you wanted to reduce the bitrates impact, uncorrectable errors arise, the predictive coding methods, such as motion compensation, make matters much worse because the errors in one video frame quickly propagate across the entire video sequence and rapidly degrade the decoded video quality.Reversible VLC's can be used to increase resilience to channel errors. If an error is detected while decoding in the forward direction, motion vector data are not completely lost as the decoder can proceed in the reverse direction; this improves error resilience of the bit stream. Furthermore, the motion vector range is extended to up to [-256, + 255.5] depending on the picture size. This is very useful given the wide range of new picture formats available in H.263+.