#4 Concept Series : What is the difference between HEVC (H.265) and H.264 (MPEG-4 AVC)
H.265 is the successor standard to H.264, aka MPEG-4 AVC and has generated huge optimism given Industry’s struggle with shortage of bandwidth, spectrum, storage and imminent need to take growing HD content for multi platform delivery. HEVC was approved by ITU-T in Jan 2013 and has been among the most discussed broadcast trends, as well as the key technology offering at NAB and IBC with product vendors and service providers flooding HEVC solutions to bring alive the cherished 4K experience.
HEVC is Big Deal …Today H.264 is the most widely accepted and adopted format in online and broadcast domain for content compression and distribution. HEVC (High Efficiency Video Coding), the new video coding standard brings promise of huge bandwidth savings of approx. 40-45% over H.264 encoded content (ref. HEVC MP and H.264 HP with similar fps) with similar quality. In addition HEVC has potential to significantly impact other areas including
- Accelerate demand and sale of 4K screens which has been largely limited due to large price difference and absence of UHD content. HEVC can offset the second challenge
- Huge opportunities from reduced bitrate requirements enabling broadcasters and OTT vendors to bundle more channels / content on existing delivery mediums
- Extend far greater video quality experience compared to H.264 encoded sequence at same bitrate
- Ability to offer higher quality video for bandwidth constrained mobile networks
- Realize differentiated and premium 4K content, multiview encoding etc..
…But HEVC Adoption is still Far. While HEVC can bring respite to content producers, aggregators, distributors and consumers with more quality content at same bitrate, the adoption curve could still be years away. Few reasons being
- Industry adoption weighs heavily on investments and with significant cost gone in H.264 gear for SD to HD migration, next expensive transition will take time. End to end deployment will require headend upgrade, workflow overhaul, re-deployment of media players (STBs, game consoles ..) with embedded HEVC hardware decoders and migration of huge content libraries from H.264 to HEVC.
- In addition to CE player, support from major technology players (Google, Adobe, Apple, Microsoft, Sony etc.) in their players, browsers, mobile and PC operating systems will determine majority adoption.
- Time to realize power efficient and real time encoders/decoders given HEVC computational overheads. Availability of affordable HEVC technology in silicon with level of reliability will be the defining milestone
What differentiates HEVC from its Predecessor
Some of the key differences between H.265 (HEVC) and H.264 (MPEG 4 AVC) are listed below
|Names||MPEG 4 Part 10 AVC (Introduced in 2004)||MPEG-H, HEVC, Part 2 (Approved in Jan 2013 )|
|Industry adoption||Dominant and accepted video codec for Terrestrial, Cable, Satellite and IPTV broadcast. (ATSC/DVB/ISDB)|
Widely used across Blu-Ray, security systems, videoconferencing , mobile video, media players, video chat etc.
|Implementation demonstration across NAB, IBC and other events starting 2012 from companies e.g. ATEME, Broadcom, Thomson , Harmonic (Cisco), Ericsson, Qualcomm etc.. Increased R&D across Encoder/Decoder /CE vendors for software and hardware based solutions|
|Key Improvement||- 40-50% bit rate reduction compared to MPEG-2|
- Led the growth of HD content delivery for Broadcast and Online
|- 40-50% the bit rate reduction at the same visual quality compared to H.264|
- Potential to realize UHD, 2K, 4K for Broadcast and Online (OTT)
|Progression||Successor to MPEG-2 Part ||Successor to MPEG 4 AVC, H.264|
| Compression Model ||Hybrid spatial-temporal prediction model|
- Flexible partition of Macro Block (MB) , sub MB for motion estimation
- Intra Prediction (extrapolate already decoded neighboring pixels for prediction)
- Introduced multi-view extension
9 directional modes for intra prediction
- Macro Blocks structure with maximum size of 16x16
- Entropy coding is CABAC and CAVLC
|Enhanced Hybrid spatial-temporal prediction model|
- Flexible partitioning, introduces Coding Tree Units (Coding, Prediction and Transform Units -CU, PU, TU)
- 35 directional modes for intra prediction
- Superior parallel processing architecture, enhancements in multi-view coding extension
- CTU supporting larger block structure (64x64) with more variable sub partition structures
- Entropy coding is only CABAC
| Specification||Support Up to 4K (4,096×2,304)|
Supports up to 59.94 fps
21 profiles ; 17 levels
|Up to 8K UHDTV (8192×4320)|
Supports up to 300 fps
3 approved profiles, draft for additional 5 ; 13 levels
| Drawbacks ||Unrealistic for UHD content delivery due to high bit rate requirements. Frame rate support restricted to 59.94||Computationally expensive (~ 300 % + ) due to larger prediction units and expensive Motion Estimation (Intra prediction with more nodes, asymmetric partitions in Inter Prediction).|
There is general euphoria and high expectations from HEVC, but historically it takes somewhere between 6-10 years before a standard become mainstream. Some stimulating questions attributing to HEVC roadmap will include
- Larger screen resolution will requires higher frame rates 60- 120 fps from current 24-30 fps, given the increase in fps, what overall efficiency savings could HEVC realistically achieve?
- Given state of bandwidth networks, growth in video coupled with multi screen delivery and absence of UHD content, will encoding existing SD/HD content with bitrate efficiency become more likely business case for HEVC rather than 4K?
- How far is HEVC adoption from broadcast industry standard specifications (DVB/ATSC) given footprint of legacy equipment and transmission infrastructure?
- What are the sector specific services which could lead the transition and embrace HEVC sooner that rest of the pack – mobile video services, OTT players? Similarly role of international events like 2014 FIFA world cup and Rio 2016 Olympics towards selective adoption?
We are bound to witness more product and service roll-outs with HEVC-related technologies and announcements from early adopters who will define the expectations for mainstream Industry. HEVC has relevance and impact across wide ranging applications in Broadcast (Cable, Satellite, IPTV), Digital Cinema, Internet streaming, content production, storage, Mobile streaming, medical imaging, video conferencing among others, but how early will the industry endorse and adopt is yet to be seen.
What is your perspective – please share your feedback, suggestions and comments!