Parallel Scalability and Efficiency of HEVC Parallelization Approaches Chi Ching Chi, Mauricio Alvarez-Mesa,, Ben Juurlink, Gordon Clare, F´elix Henry, St´ephane Pateux and Thomas Schierl IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS FOR VIDEO TECHNOLOGY

Outline Introduction Video codec parallelization approaches Coding efficiency analysis Experimental evaluation Conclusions

Introduction While the single-core processor can decode a 1080p H.264/AVC video in real-time, it is very unlikely that processor performance will decode a 2160p50 HEVC video in real-time. To obtain real-time HEVC decoding performance, parallelism is no longer an option but a necessity.

Introduction H.264/AVC supports slice parallelization. It may not achieve real-time if it receives a video with one or a few slices per frame. The main parallelization approaches currently included in the HEVC draft (Tiles and Wavefront Parallel Processing[WPP]). This paper presents a approach called Overlapped Wavefront(OWF).

Previous parallelization strategies Frame-level parallelism Slice-level parallelism Macroblock-level parallelism

Frame-level parallelism Frame-level parallelism consists of processing multiple frames at the same time. Frame-level parallelism is sufficient for multicore systems with just a few cores. If due to fast motion, motion vectors are long, there is little parallelism.

Slice-level Parallelism Each frame can be partitioned into one or more slices. Slices in a frame are completely independent from each other and therefore they can also be used for parallel processing. It is useful for a frame with a few slices but not one slice per frame.

Macroblock-level Parallelism

Parallelization Strategies in HEVC Tiles Wavefront Parallel Processing (WPP) Overlapped Wavefront (OWF)

Tiles

Tiles The number of tiles and the location of their boundaries can be defined for the entire sequence or changed from picture to picture. Compared to slices, Tiles have a better coding efficiency. The rate-distortion loss increases with the number of tiles. because Tiles allows picture partition shapes that contains samples with a potential higher correlation than slices

Wavefront Parallel Processing (WPP)

Overlapped Wavefront (OWF) When a thread has finished a CTB row in the current picture and no more rows are available it can start processing the next picture instead of waiting for the current picture to finish. The support this approach, the motion vector is contrained to ¼ of picture height.

Overlapped Wavefront (OWF)

Coding efficiency analysis

Coding efficiency analysis

Experimental evaluation Environment

Experimental evaluation

Experimental evaluation

Experimental evaluation

Experimental evaluation

Conclusions We present a detailed performance comparison of the main approaches, namely WPP ,Tiles and OWF. Tiles performance 7% higher than WPP on average at 12 cores. The proposed OWF 28% higher on average than Tiles. Achieve real-time performance for 1080p50 videos, but “only” 25.4 fps for 2160p.