Doctor Who: Twice Upon a Time 4K UHD (2017)

[Geoff D]

Originally Posted by morphinapg

Yeah that's really weird. This gives me an interesting idea though. For short run length releases like this, particularly ones with 2K masters, could it theoretically be possible to include both a standard Blu-ray and UHD version on a single 50GB disc? Sort of how they included 3D and 2D on the same disc. Like, if you only have a standard Blu-ray player, it just defaults to the standard 1080p menu and titles, but if you have a UHD player, the menu will intelligently detect that and load a separate menu that allows for UHD playback?

Nope. The disc itself has to be authored with one format spec or another, BD or UHD. You could put two separate encodes on there for sure, even solely 1080p SDR content if you were feeling perverse, but if it's put onto a UHD-authored BD50 it still wouldn't play on anything but a UHD player. UHD Blu does have another 'dual stream' encoding feature whereby you can set two video streams (SDR and HDR) to the same audio so you don't have to double up the entire encode, audio and all, but again it would be playable on UHD players only.

(Even 3D Blu didn't work by storing two complete versions on the disc. The MVC (multi view coding) method works by encoding the left eye onto disc as a standard 2D stream while the right eye is encoded as the difference data between left and right and isn't a viewable video stream as such. This data stream is decompressed and reconstituted by the player and sent out as a 'frame packed' 1920x2205 image for the TV to unpack into the final 3D version.

And even though the left eye was always intended to be 2D compatible in the spec it's not the actual final 2D version of the movie anyway, it will contain whatever colour grading and visual anomalies (floating windows, conversion artefacts etc) that were designed for the 3D version, hence several studios choosing to lock out the left eye from 2D playback.)