HEVC - High Efficiency Video Coding

High Efficiency Video Coding (HEVC) is the most recent standardized video compression technology. It is developed by the Joint Collaborative Team on Video Coding (JCT-VC) of the ITU-T Visual Coding Experts Group (VCEG) and the ISO/IEC Moving Pictures Experts Group (MPEG). The first version of the new standard has recently been consented as Recommendation ITU-T H.265 and will shortly been approved by ISO/IEC as ISO/IEC 23008-2 (MPEG-H part 2). As its most important feature, HEVC provides around 50% bit-rate reduction while maintaining the same subjective video quality relative to its predecessor H.264/AVC.

The Image & Video Coding Group has contributed a couple of important coding tools to the new HEVC standard, as listed below. Also, in cooperation with the Multimedia Communication Group at HHI, some useful high-level features for ultra low-delay coding and parallelization have been developed and contributed.

Just like its predecessor H.264/AVC, High Efficiency Video Coding (HEVC) is a hybrid video-compression scheme consisting of block-based prediction followed by block-based transform coding of the prediction residual. In HEVC, however, the block-based paradigm has undergone an evolution in terms of increased flexibility of block partitioning both for prediction and transform coding by incorporating proposals which are based on suitable quadtree-based techniques.

Further Information

The partitioning for the transform using the residual quadtree (RQT) is flexible as for the coding tree. Comparing to the predecessor standard H.264/AVC, the transforms are increased and they are ranged from 4×4 dyadically up to 32×32.

Further Information

An ideal filter for fractional displacement of a reference signal retains all frequencies and introduces constant phase shift for all frequencies. However, due to various effects in signal acquisition and noise, the efficiency of MCP is limited. We proposed a spline based framework for MCP. The output pictures are first converted into spline coefficients using a prefilter and stored in the reference picture buffer. Then, during the MCP stage, fractional displacements are generated using interpolation filters with short support. A detailed analysis of the coding efficiency, complexity and memory bandwidth is provided. Average bit-rate savings of around 7 - 8% compared to the scheme in H.264/AVC and around 2 - 3% compared to the scheme in H.265/HEVC are observed.

Further Information

Algorithms for compression of image- or video-signals inevitably comprise a form of signal modeling. However, the statistics of natural image- or video-signals are usually non-stationary, and the whole signal can hardly be characterized efficiently by a single model. Hence, pictures and their corresponding sample arrays are usually decomposed into blocks, such that each block is associated with one of a set of simple models and corresponding model parameters. The emerging video compression standard HEVC employs quadtree-based partitioning for motion compensated prediction and transform coding. To eliminate the redundancies among motion parameters characterized above, the leaf merging concept was integrated into HEVC in form of a block merging algorithm.

Further Information

With transform block sizes of up to 32×32, adjustments to the original binarization and context modeling stages of CABAC in H.264/AVC were inevitable. These adjustments were primarily made in order to reduce complexity in many aspects such as, e.g., reduced number of context models, coherent logic for all transform block sizes, and increased throughput. Moreover, the use of local templates for context modeling is intended to improve coding efficiency relative to a straightforward extension of the CABAC scheme in H.264/AVC for transform blocks larger than 8×8.

Further Information

• Benjamin Bross has been appointed as Editor of the JCTVC project
• Thomas Wiegand has been appointed as Co-Editor of the JCTVC project.
• Karsten Sühring has been appointed as Co-Chair for the HM reference software.