High Efficiency Video Coding

Description

High Efficiency Video Coding (HEVC), also known as H.265 and MPEG-H Part 2, is a video compression standard developed by the Joint Collaborative Team on Video Coding (JCT-VC). Within the 3GPP ecosystem, it is standardized as a codec for multimedia telephony, streaming, and broadcast services. The codec's architecture is based on a block-based hybrid video coding approach, similar to its predecessor AVC, but with significant enhancements. It uses advanced techniques like larger and more flexible block structures (Coding Tree Units up to 64x64 pixels), improved intra-prediction with 35 directional modes, enhanced motion vector prediction and merge techniques, and more sophisticated in-loop filters such as Sample Adaptive Offset (SAO). These improvements allow it to achieve approximately 50% bitrate reduction for the same perceptual video quality compared to AVC.

In a 3GPP network, HEVC operates within the media processing and delivery framework defined for services like Multimedia Telephony Service for IMS (MTSI), Packet-Switched Streaming Service (PSS), and Multimedia Broadcast/Multicast Service (MBMS). The codec is integrated into end-user devices (UEs) and network elements like the Media Resource Function Processor (MRFP) for transcoding or the Broadcast-Multicast Service Center (BM-SC) for broadcast. The encoding process involves partitioning each picture into Coding Tree Units (CTUs), which are then recursively split into Coding Units (CUs) using a quadtree structure. Prediction (intra or inter), transformation, quantization, and entropy coding are then applied to these CUs. The resulting bitstream is packaged according to 3GPP-defined formats, such as the ISO Base Media File Format (ISOBMFF) for streaming or the Real-time Transport Protocol (RTP) for conversational services.

The role of HEVC in the network is to enable high-efficiency video applications, which are a primary driver of mobile data traffic. For service providers, it reduces the bandwidth and storage costs associated with delivering high-resolution video. For users, it enables higher quality experiences, such as 4K Ultra HD video on mobile devices, without proportionally increasing data consumption. 3GPP specifications define the profiles, levels, and carriage formats for HEVC to ensure interoperability across devices and networks. This includes support for various color spaces, high dynamic range (HDR), and 360-degree video, making it a versatile codec for next-generation multimedia services.

Purpose & Motivation

HEVC was created to address the exponential growth of video traffic on mobile networks and the limitations of the previous AVC (H.264) standard. As consumer demand shifted towards higher resolution video (HD, 4K, and eventually 8K) and new applications like virtual reality emerged, AVC's compression efficiency became a bottleneck. Delivering such content would require unsustainable amounts of network bandwidth and storage, increasing costs for operators and potentially degrading user experience due to congestion. The primary motivation was to develop a codec that could halve the required bitrate for equivalent quality, thereby future-proofing networks for the video-centric data era.

Historically, each new generation of video codec (e.g., MPEG-2, AVC) has delivered a significant leap in compression efficiency. HEVC continues this trend, initiated by the ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Moving Picture Experts Group (MPEG) through their joint collaboration. Its adoption into 3GPP, starting in Release 12, was driven by the need to standardize its use within IMS-based and streaming services. This ensured a unified, interoperable approach for video delivery across global mobile networks, preventing fragmentation. By standardizing HEVC, 3GPP enabled operators to deploy advanced video services efficiently, supporting business models like mobile TV, video-on-demand, and high-quality video calling, which are central to the 4G and 5G service portfolios.

Key Features

• Coding Tree Unit (CTU) structure supporting blocks up to 64x64 pixels for more efficient representation of homogeneous areas
• Advanced motion vector prediction including Merge mode and Advanced Motion Vector Prediction (AMVP) to reduce inter-prediction overhead
• Sample Adaptive Offset (SAO) in-loop filter that reduces banding artifacts and improves subjective quality
• Support for parallel processing tools like Tiles and Wavefront Parallel Processing (WPP) to leverage multi-core architectures
• Wide range of profiles and levels supporting mainstream, high-dynamic-range (HDR), and scalable video coding
• Integration with 3GPP media delivery frameworks including ISOBMFF for streaming and RTP for real-time communication

Evolution Across Releases

Defining Specifications