What is H265/HEVC?
H.265, also known as HEVC (High Efficiency Video Coding), is a video compression standard designed to provide higher compression efficiency than its predecessor, H.264 (AVC).
It was developed by the ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Moving Picture Experts Group (MPEG).
Key Features:
Higher Compression Efficiency:
H.265 can reduce file sizes by about 50% compared to H.264 for the same level of video quality.
This makes it ideal for streaming high-resolution videos (e.g., 4K, 8K) over limited bandwidth.
Support for Higher Resolutions:
Designed to handle video resolutions up to 8K Ultra HD (8192×4320).
Improved Bitrate Efficiency:
Allows for smoother streaming and less buffering, especially on low-bandwidth connections.
Enhanced Coding Techniques:
Uses more advanced block structures (up to 64×64 pixel blocks compared to H.264’s 16×16).
Includes better motion compensation and prediction algorithms.
Support for HDR (High Dynamic Range):
Enables more vibrant colors and better contrast for compatible displays.
How Does H.265/HEVC Work?
H.265 (HEVC) works by compressing video data to reduce file size without significantly compromising video quality.
It does this through a series of advanced encoding techniques that build on those used in H.264, with improvements for greater efficiency.
Coding Tree Units (CTUs):
H.265 divides a frame into Coding Tree Units (CTUs), which are the building blocks of the video. CTUs can be up to 64×64 pixels (compared to 16×16 blocks in H.264), allowing for more flexible and efficient compression. Each CTU can be further subdivided into smaller units to adapt to complex image areas (like edges or textures).
Advanced Features in H.265
a. Larger Block Sizes:
CTUs allow for more efficient compression of uniform areas (e.g., skies or walls).
b. Improved Motion Prediction:
More sophisticated motion compensation methods predict movement more accurately.
Supports up to 33 directional predictions, compared to 9 in H.264.
c. Adaptive Bitrate Allocation:
Allocates more bits to complex parts of a video (like detailed textures) while using fewer bits for simpler areas.
d. Deblocking and Filtering:
H.265 applies post-processing filters to smooth out compression artifacts (like blockiness) and improve visual quality.
By combining these techniques, H.265 achieves:
Up to 50% better compression efficiency than H.264.
Support for high resolutions (4K, 8K) without a massive increase in file size.
Enhanced streaming performance, especially on lower-bandwidth connections.
Bitrate Vs File Size Vs Quality
If you’ve tried compressing a video using H.265, your first instinct might be to use the same bitrate you would for H.264, expecting a file size reduction of 25–50%.
However, this won’t be the case—you’ll likely end up with a file size similar to what you’d get with H.264.
Why? It’s because you’re essentially asking your computer to process the same amount of data, whether encoding a two-minute video at 20 Mbps with H.264 or H.265. While H.265 is much more efficient at compressing video data, its true advantage lies in its ability to maintain the same quality at a lower bitrate.
To leverage this efficiency and reduce file size, you should lower the bitrate when exporting with H.265.
A good rule of thumb is to decrease the bitrate by around 33%, which allows you to achieve the same video quality while benefiting from the 25–50% compression savings that H.265 offers.
Refer to the following table for guidance.
H265 is only required if the content is 4k or above and is not required for Images. If the video is not 4K or greater the application will still play the content without any issues.