Codecs Revisited: What Are H.264 And H.265?

Following on from earlier blogs on the subject, this post looks at high performance codecs that are popular in AV pro circles, with the focus on H.264 and H.265. Read on…

• What is H.264?
• What is H.265?
• What's the difference between H.264 and H.265?
• What other high-performance codecs are out there?

WHAT IS H.264?

When we talk about video compression, the codec that often comes to mind is H.264, aka MPEG-4 Part 10 Advanced Video Codec (MPEG-4 AVC). This industry standard for video compression technology was originally developed by ITU, the International Telecommunications Union, and ISO, the International Organisation for Standardization. First published in 2003, it is based on the concept of MPEG-2 and MPEG-4.

Some of the best features about this video codec are:

• Good quality compressed video output
• Good flexibility in transmitting and preserving the video
• Good quality image at the compressed bitrate

In H.264 the video encoder initialises multiple processes such as prediction, transform, and encoding in order to create an H.264 bitstream. It uses a block-oriented standard with motion compensation to process video frames. The resulting macroblocks are16 x 16 pixel samples, subdivided into transform and then prediction blocks. The video decoder processes the inverse transform and reconstruction to create a decoded video sequence for distribution.

Where will you find H.264? Some of the main applications of this video codec are:

• High definition DVDs, such as HD-DVD and Blu-Ray
• High definition TV broadcasting, especially in Europe
• Apple products
• NATO and US Department of Defense video applications
• Mobile TV broadcasting
• Internet sources (iTunes, YouTube, for example)
• Video conferencing

WHAT IS H.265?

H.265 is also referred to as High-Efficiency Video Coding (HEVC) and delivers higher quality video at the same bitrate as H.264. It has the potential to support resolutions of 8192 x 4320 pixels (bear in mind that 8K UHD is 7680 x 4320). H.265 was developed by the Joint Collaborative Team on Video Coding (JCT-VC), and collaboration between the ISO/IECMPEG and ITU-TVCEG.

There are four versions of H.265 video codec:

• Version 1: It was the first version of H.265 codec which was released on April 13, 2013.
• Version 2: It was the second version of H.265 codec and was released on October 29, 2014.
• Version 3: This version of H.265 codec and was released on April 29, 2015.
• Version 4: This version of H.265 codec and was released on December 22, 2016.

Best features of H.265:

• It provides higher and much better compression ratio compared to H.264.
• It is also used in high-resolution movies say 2K or 4K.
• It is also helpful in reducing the bandwidth with larger resolutions.

This codec uses a different macroblock-encoding method, Coding Tree Units. CTU processes information with greater coding efficiency (the lowest bitrate while maintaining video quality) and supports 64 x 64 macroblocks.

Applications:

• H.265 supports different color spaces such as generic film, NTSC, PAL, Rec. 601, Rec. 709, Rec. 2020, Rec. 2100, SMPTE 170M, SMPTE 240M, sRGN, sYCC and xvYCC.
• Next-generation HDTV displays and content capture systems.

What's the difference between H.264 and H.265?

So what does H.265 offer compared to H.264…

• The compression ratio of H.265 is almost double that of H.264.
• H.264 provides support for 16 x 16-pixel macroblocks whereas H.265 provides support for 64 x 64-pixel macroblocks.
• Video compression is highly dependent upon prediction motion between frames. H.265 offers significant improvements in prediction motion compared to H.264.
• The intraframe prediction function of H.265 is more descriptive than H.264. This means H.265 can allow for 33 directions of motion whereas H.264 only allows for nine directions of motion.
• H.265 implements separate tiles and slices which are decoded independently.
• H.265 provides support for resolutions up to 8192 x 4320 pixels (including 8K UHD) whereas H.264 does not provide support for such resolutions.
• H.265 requires much less bandwidth as compared to H.264 codecs. For instance, H.264 requires 32 mbps internet speed to broadcast 4K video while HEVC can easily do the same in just 15mbps.

What other high performance codecs are out there?

Yes, there are some alternatives available to codec standards like H.265 and H.264, such as Cinegy’s Daniel2 codec. The self-proclaimed “world’s fastest video codec” was designed for recording from camera sources, editing and playout. A GPU codec, it is said to accelerate the production chain significantly and is getting compared to AVID’s DNxHR, Apple’s ProRes, JPEG2000 or Sony’s XAVC.

The technical specification of Daniel2 codec is listed as follows:

• The color space ranges from 4:2:2 to 4:4:4:4 (YUV to RGBA).
• Color depth ranges from 8 to 12 bit along with 16bit.
• Extremely low decoding latency (about less than 1 ms for 8K)
• Support for multi-generation re-compression without artefacts.
• Freely selectable compression factor.
• Variable bit rate, constant bit rate or constant quality encoding.
• Supports lossy or lossless encoding modes.
• Assistance for Nvidia CUDA acceleration and CPU fallback for VM or cloud w/o GPU.
• 64 bit Windows, Linux, and Mac OS.
• Intelligent alpha channel support for small file sizes.
• Support for IP video that is the most suitable codec especially for low-latency, high-quality compressed IP video transmission.

Previous blogs in this series: Is this a codec (or a container) which I see before me?

Codecs revisited: H.264 and H.265

More reading:

Uncompressed video playback