A probabilistic-based CU size pre-determination method for parallel processing of HEVC encoders

The advent of the state-of-the-art video coding standard, High Efficiency Video Coding (HEVC) is expected to bring great changes to relevant fields of broadcasting, storage and communications. HEVC achieves higher coding gains compared to its previous video coding standards in terms of rate-distortion (R-D) performance with various improved coding tools. This leads to heavy computational complexity and costs to HEVC encoders and these comes as strong restrictions specially to develop H/W types of encoders that are more preferred for real-time based applications and services. In particular, the quad-tree based coding unit (CU) structures with various sizes are known to contribute to achieving high coding gains of HEVC. However, RD cost calculation for mode decision with all CU sizes cannot normally be considered in the H/W HEVC encoders for real-time operation. To overcome this, a CU size pre-determination method based on a probabilistic decision model fit to implement H/W HEVC encoders is proposed in this paper. All available CU sizes are checked before inter prediction and unnecessary CU sizes are excluded from inter prediction according to the decision model. Then inter prediction with the reduced number of CU sizes can be performed in parallel with pipeline structures. The experimental results show that the proposed method effectively determines the necessary CU sizes with negligible coding loss of 1.57% for LD (Low-delay) coding structure and 1.08% for RA (Random access) coding structure, respectively in BD-BR.