A two-level variable bit rate (VBR) control algorithm for hierarchical video coding, specifically tailored for the new High Efficiency Video Coding (HEVC) standard, is presented here. A long-term level monitors the current bit count along a sliding window of a few seconds, comprising several intra-periods (IPs) and shifted on an IP basis. This long-term view allows the accommodation of the naturally occurring rate variations at a slow pace, avoiding the annoying sharp quality changes commonly appearing when non-sliding window approaches are used. The bit excesses or defects observed at this level are evenly delivered to a short-term level mechanism that establishes target bit budgets for a narrower sliding window covering a single IP and shifting on a frame basis. At this level, an adequate quantization parameter is estimated to comply with the designated target bit rate. Recommended test conditions as well as two few minutes long video sequences with scene cuts have been used for the assessment of the proposed VBR controller. Comparisons with a state-of-the-art rate control algorithm have produced good results in terms of quality consistency, in exchange for moderate rate-distortion performance losses.
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