The Blu-Ray Disc Association (BDA), which is the official body that decides Blu-ray specifications, has set a standard that will allow UltraHD (3840 x 2160) material to be stored on Blu-ray discs. The new format for UltraHD Blu-ray will be a 66 GB dual-layer disc and a 100 GB triple-layer Blu-ray disc. Video will be encoded with h.265 or HEVC (High Efficiency Video Codec). Audio will remain lossless Dolby TrueHD and DTS HD-Master Audio.
Previously, Blu-ray used 4:2:0 color, while the new 4K Blu-ray supports 4:4:4 (even though most TVs and most A/V receivers/processors don't yet support 4:4:4). The new Blu-ray UltraHD specification ups the old 8-bit sampling to support 10-bit sampling.
There is also support for HDR, or High Dynamic Range. UltraHD Blu-ray discs will enable HDR formats, but precisely which HDR format will be supported has not been disclosed.