All-zero block-based optimization for quadtree-structured prediction and residual encoding in high efficiency video coding

High Efficiency Video Coding (HEVC) outperforms H.264 High Profile with bitrate saving of about 43%, mostly because block sizes for hybrid prediction and residual encoding are recursively chosen using a quadtree structure. Nevertheless, the exhaustive quadtree-based partition is not always necessary. This paper takes advantage of all-zero residual blocks at every quadtree depth to accelerate the prediction and residual encoding processes. First, we derive a near-sufficient condition to detect variable-sized all-zero blocks (AZBs). For these blocks, discrete cosine transform (DCT) and quantization can be skipped. Next, using the derived condition, we propose an early termination technique to reduce the complexity for motion estimation (ME). More significantly, we present a twodimensional pruning technique based on AZBs to constrain prediction units (PU) that contribute negligibly to rate-distortion (RD) performance. Experiments on a wide range of videos with resolution ranging from 416 × 240 to 4k × 2k, show that the proposed scheme can reduce computational complexity for the HEVC encoder by up to 70.46% (50.34% on average), with slight loss in terms of the peak signal-to-noise ratio (PSNR) and bitrate. The proposal also outperforms other state-of-the-art methods by achieving greater complexity reduction and improved bitrate performance.