Rate-constrained two-layer coding of H.261 video

This paper describes a proposed method for two-layer coding of low-rate H.261-encoded video subject to a rate constraint. A refinement scheme is utilized where the base layer consists of H.261 video encoded at some low rate, and the refinement layer consists of the difference between the original video and the H.261-encoded video, rate constrained so that the total bit rate of the two layers equals some desired higher rate. We show that the proposed method provides significant improvement over the lower rate baseline H.261-encoded scheme, as expected, both quantitatively (in terms of an error measure) as well as qualitatively (in terms of perceived picture quality). We also show that the additional computational costs incurred are typically held to around 10-20% at the encoder, with varying costs at the decoder depending on the specific method implemented. Finally, we show that the proposed scheme offers a more graceful degradation in performance in the presence of packet loss when compared to single-layer H.261