I've mentioned it before, but everything is more finalized now. Blu-ray Disc Association has announced that is has started licensing the UHD 4K video format on August 24, with expected "product announcements from various companies" coming this holiday season.

The format allows three sizes: 50GB with 82 Mbit/s, 66GB with 108 Mbit/s, and 100GB with 128 Mbit/s. Ultra HD or 4K video is the focus, 3D will also be enabled on UHD Blu-rays. This is only for 3D films in HD, however - there are no plans for Ultra HD 3D films. In terms of audio, it's all about Dolby Atmos and DTS:X - will be  supported.

In addition to that lovely  3840x2160 resolution, Ultra HD Blu-ray offers frame rates of up to 60 frames per second, high dynamic range video will also be available. Ultra HD Blu-ray players will be backwards compatible with standard 1080p Blu-ray formats.