Abstract
This paper proposes a sub-frame layer RDO algorithm to further improve coding performance of low-delay hierarchical prediction structure in High Efficiency Video Coding. In the proposed algorithm, each frame is segmented into two sub-frames according to motion intensity, and a sub-frame layer is taken as a basic optimizing unit. An inter-frame dependency model is proposed to quantify inter-frame dependency of a frame or a sub-frame. The proposed inter-frame dependency model is composed of two parts, Laplace distribution based direct inter-frame dependency model and distortion propagation chain. The direct inter-frame dependency model is used to evaluate dependency caused by direct reference, and the distortion propagation chain shows the relationship between direct reference and indirect reference. With quantified inter-frame dependency, Lagrange optimization is then used to solve the optimal $\lambda $ -QP pair for each sub-frame layer in frame layer 1 (L1) to frame layer 4 (L4). For frame layer 0 (L0), additional L0 frames are adaptively inserted according to inter-frame dependency of the previous L0 frame, and the optimal $\lambda $ -QP pair for each sub-frame in L0 is solved using Lagrange optimization. When peak signal to noise ratio is used as quality criterion, the proposed algorithm achieves 7.0% and 7.0% bit-rate reduction with lowdelay_P_main (LDP) and lowdelay_main (LDB) configurations respectively; when structural similarity is used as quality criterion, the proposed algorithm achieves 13.3% and 13.1% bit-rate reduction with LDP and LDB configurations respectively.
Highlights
In hybrid video coding, a specific video coding standard, such as High Efficiency Video Coding (HEVC) [1], defines the limitation of compression efficiency, while rate distortion optimization (RDO) guides how to achieve the limitation
The optimal coding scheme can be obtained by solving the following unconstrained problem, min (J ), where J = Dpi + λg Rpi pi pi where J is rate distortion (RD) cost; λg is global Lagrange multiplier; pi is frame with picture order count (POC) of i; The associate editor coordinating the review of this manuscript and approving it for publication was Gangyi Jiang
A frame is segmented into two sub-frames, i.e., high motion content (HC) and low motion content (LC)
Summary
A specific video coding standard, such as High Efficiency Video Coding (HEVC) [1], defines the limitation of compression efficiency, while rate distortion optimization (RDO) guides how to achieve the limitation. The direct inter-frame dependency model is built based on Laplace distribution to quantify direct impact of distortion of a reference frame/sub-frame on distortion and bits of the target frame/sub-frame. A direct inter-frame dependency model based on Laplace distribution is built to analyse direct impact first; distortion propagation chain in LD-HPS is established to show the relationship between direct impact and indirect impact; total impact of a frame is obtained with the help of distortion propagation chain. In this case, p0 is the only reference frame of p1, and there is no indirect dependency between p0 and p1, which means the total impact of p0 on distortion of p1 equals to the direct impact, i.e., TIpd0is,p1 = DIpd0is,p1. Compared with 8 × 8 block granularity content segmentation, small burr is filtered out by CTU granularity content segmentation
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