H.265, also known as High Efficiency Video Coding (HEVC), is a video codec for compressing high-resolution digital video. It is a successor format to the older H.264 codec, offering better compression that results in a similar quality video at half the effective bitrate. It supports resolutions up to 8K UHD and deep color depths for HDR video.
The H.265 codec uses inter-frame media compression to remove unnecessary data from a video stream. It compares each video frame to the previous frame and encodes only the changes between the two. It analyzes each frame by dividing it into blocks up to 64x64 pixels in size. These blocks, called coding tree units (CTUs), can be subdivided into smaller blocks to encode highly-detailed areas.
H.265 is one of the most common formats for downloading and streaming 4K video. Its higher compression ratio compared to H.264 means that 4K video files can take up less storage space or streaming bandwidth. For example, a 4K video stream using H.264 requires a bitrate of about 30 Mbps, while the same quality level using H.265 only requires 15 Mbps. It also supports 10- and 12-bit color depths by default, instead of as an optional feature, making H.265 a better choice for distributing HDR video.
Since H.265 is more complex than H.264, decoding it requires more computing power. Older, less powerful devices may struggle to play back a video at all. However, most CPUs and GPUs made after 2016 include built-in hardware support for encoding and decoding H.265 video streams. The processors in video streaming devices designed for 4K content, like the Apple TV and Roku Ultra, are also optimized for H.265 video.