Pareto-Based Method for High Efficiency Video Coding With Limited Encoding Time

Several different methods have been investigated in recent years, aiming at computational complexity reduction and scaling of High Efficiency Video Coding (HEVC) software implementations. However, maintaining the encoding time per frame or group of pictures (GOPs) below an adjustable upper bound is still an open research issue. A solution for this problem is devised in this paper based on a set of Pareto-efficient encoding configurations, identified through rate-distortion-complexity analysis. The proposed method combines a medium-granularity encoding time control with a fine-granularity encoding time control to accurately limit the HEVC encoding time below a predefined target for each GOP. It is shown that the encoding time can be kept below a desired target for a wide range of encoding time reductions, e.g., up to 90% in comparison with the original encoder. The results also show that compression efficiency loss (Bjøntegaard delta-rate) varies from negligible (0.16%) to moderate (9.83%) in the extreme case of 90% computational complexity reduction.

I. Introduction

The High Efficiency Video Coding (HEVC) standard was finished in 2013 by the Joint Collaborative Team on Video Coding (JCT-VC), a joint activity of International Telecommunication Union Video Coding Experts Group and International Organization for Standardization/International Electrotechnical Commission Moving Picture Experts Group [1]. The standard became the state of the art method for video compression and is expected to gradually substitute its predecessor, the H.264/Advanced Video Coding (AVC) standard, in consumer equipment able to receive, display, capture, and transmit high-resolution video. When compared with H.264/AVC High profile (HP), HEVC Main profile reduces bit rates by 40% on average, maintaining a similar objective reconstructed image quality [2]. However, the improved compression efficiency of HEVC is obtained at the expense of a significant increase in computational complexity, mainly resulting from much more intensive processing tools, nested partitioning structures and optimization algorithms dealing with larger amounts of data. According to [3], the encoding computational complexity of HEVC is higher than H.264/AVC HP from 9% to 502%, depending on the HEVC Test Model (HM) [4] configuration used. Such wide variation in computational complexity is due to the large number of optional coding tools that can be used within the standard compliance bounds. In [2], the computational complexity of HEVC was found to be 40% higher than that of H.264/AVC HP when only the most important coding tools are enabled.