Algorithm and Architecture Design of the H.265/HEVC Intra Encoder

Improved video coding techniques introduced in the H.265/High Efficiency Video Coding (HEVC) standard allow video encoders to achieve better compression efficiencies. On the other hand, the increased complexity requires a new design methodology able to face challenges associated with ever higher spatiotemporal resolutions. This paper presents a computationally scalable algorithm and its hardware architecture able to support intra encoding up to 2160p@30 frames/s resolution. The scalability allows a tradeoff between the throughput and the compression efficiency. In particular, the encoder is able to check a variable number of candidate modes. The rate estimation based on bin counting and the distortion estimation in the transform domain simplify the rate-distortion analysis and enable the evaluation of a great number of candidate intra modes. The encoder preselects candidate modes by the processing of 8 x 8 predictions computed from original samples. The preselection shares hardware resources used for the processing of predictions generated from reconstructed samples. To support intra 4x4 modes for the 2160p@30 frames/s resolution, the encoder incorporates a separate reconstruction loop. The processing of blocks with different sizes is interleaved to compensate for the delay of reconstruction loops. Implementation results show that the encoder utilizes 1086k gates and 52-kB on-chip memories for TSMC 90 nm. The main reconstruction loop can operate at 400 MHz, whereas the remaining modules work at 200 MHz. For 2160p@30 frames/s videos, the average BD-rate is 5.46% compared with that of the HM software.