H.265: high-quality mobile video or low-bandwidth video?

The International Telecommunications Union (ITU) has announced the first stage for H.265 video codec standard has been completed and that the new codecs will be twice as efficient in video compression, requiring half the bandwidth for the same quality as H.264 compressed video.

The new standard is intended to improve video on smartphones, tablets, TVs, and other devices as screen resolutions increase over the next 10 years, while reducing the burden on wired and wireless networks. Notice that today’s estimations point to half of all network traffic to be video, which should go up to as much as 90 percent of all network traffic by 2015.

The current specification, also known as MPEG-4, is the most used video-compression standard in the world, according to ITU. It’s the coding and decoding system for more than 80 percent of all Web video and is used to deliver high-definition video over broadcast, cable, satellite, and Internet TV. H.264 is also used in mobile phones, video conferencing, digital storage, and Blu-ray discs.

Informally known as ‘High Efficiency Video Coding’ (HEVC), H.265 has been drafted in August of 2012, supporting resolutions up to 7680-by-4320, enough for the new Ultra HD (4K and 8K) resolutions. Work is also underway to develop an extension of H.265 for stereoscopic and 3D video coding.

The new standard is expected to be more efficient than its predecessor, H.264 Advanced Video Coding, but how much better it will perform is a crucial question to understand if it will be enough to justify widespread industry adoption.

Studies (see Comparison of Compression Performance of HEVC Working Draft 4 with AVC High Profile by Bin Li, Gary Sullivan and Jizheng Xu and Comparison of the Coding Efficiency of Video Coding Standards – Including High Efficiency Video Coding (HEVC) by Jens-Rainer Ohm, Gary J. Sullivan, Heiko Schwarz, Thiow Keng Tan, and Thomas Wiegand) show that on average, H.265 outperforms H.264 by 39% for random access scenarios (e.g. broadcast) and by 44% for low delay scenarios (e.g. video calling). Meaning that H.265 codec can achieve the same quality as H.264 with a bit rate saving of around 39-44% bandwidth.

What most media reports seem to have focused on is the potential effect that H.265 will have on bringing us closer to 4K video resolution in OTT delivery, speculating that H.265 will allow 4K video to be delivered over the Internet at bit rates between 20 and 30 Mbps. But given the current state of video streaming technology, we can actually be able to deliver 4K video at lower bit rates when the time comes for 4K streaming. Moreover, as many studies show, the law of diminishing returns applies to video/image resolution too – if you sit at a fixed distance from your video display device eventually you will no longer be able to distinguish the difference between 720p, 1080p and 4K resolutions due to your eye’s inability to resolve tiny pixels from a certain distance.

Historically, bit rates used for OTT video delivery and streaming have been much lower than those used in broadcasting, consumer electronics and physical media. On average:

  • Digital broadcast HDTV: ~19 Mbps for video (in CBR mode);
  • Blu-ray (1080p): ~15-20 Mbps (in 2-pass VBR mode);
  • Streaming video (720p): ~2.5-3.5 Mbps;
  • Streaming video (1080p): ~5-6 Mbps.

Whereas Blu-ray aims to provide a high-definition movies, streaming/OTT is completely driven by the economics of bandwidth and consequently only gives us video at the minimum bit rate required to make the video look generally acceptable. Considering that currently, 1080p video is being widely streamed online using H.264 compression at 6 Mbps, then 4K (4096×2304) video could probably be delivered at bit rates around 18-20 Mbps using the same codec and similar quality levels. Switching from H.264 to H.265 compression we can expect 4K video at bit rates closer to 12-15 Mbps!

Posted on Feb 11, 2013