The 4K stage production of the National Theatre's War Horse claimed a number of firsts when it aired on February 27. Not only was it the first live-to-cinema 4K transmission, it was the first commercial run for the format in which cinema-goers at Chelsea's Curzon paid to see the 180-minute event. It also necessitated the world’s first high frame rate 4K Digital Cinema Package (DCP).
National Theatre Live (NT Live) broadcast War Horse from the New London Theatre to more than 1,000 cinemas worldwide – most live but with many also showing delayed 'live' screenings. All but one of those was an HD broadcast, but the significance of the sole 4K transmission points the way to the future.
Creative Broadcast Solutions (CBS), technical producer for NT Live, with NEP Visions, NT Live’s long-term OB partner and satellite service provider Links Broadcast partnered with Sony to deliver the event, which is NT Live's 36th stretching back to 2009.
“We regularly cover NT Live productions in HD, but the National Theatre thought that War Horse was such an important show that it should ideally be captured with large format cameras,” explained David O'Carroll, technical projects manager, NEP Visions.
“What was equally important was maintaining the HD workflow since that feed was going to the majority of cinemas. We built a 4K layer into the flypack installed onsite, complemented by an audio truck and a second truck for graphics, subtitles and autocue.”
Six F55 CineAlta cameras equipped with Fujinon Cabrio lenses fed 4K video into BPU4000 fibre adapters, which generated 4K and HD signals simultaneously. The feeds were presented at a Sony MVS-8000X switcher as four HD 3G signal (quad 4K) to create a 4K mix with graphics. There was also an HD version the same and another HD path with subtitles.
“4K live to a projector had never been done before so we had to do a lot of testing to get the suitable video bitrate,” said Chris Bretnall, technical producer for NT Live at Creative Broadcast Solutions. “Typical HD relays that go to cinemas use approximately 18-19Mbps within a 36Mhz carrier. Now we are getting over 100Mbps within the same bandwidth.”
The incoming signal was downlinked at the Curzon via a 1.8M Links Broadcast receive antenna, which was fed into Adtec RD70 receiver decoders and delivered to the projector.
The live feed was encoded in standard Digital Cinema Initiatives (DCI) compliant DCP. In charge of this were digital cinema lab Soho Digital CinemaSDC, who were presented with a huge challenge. Currently 4K HFR is only a proposal in the recommendations of the DCI, the governing body that sets digital cinema standards.
The Hobbit 3D films, for example, were shown at 24p for each 'eye', whereas War Horse was shot and screened as a single eye 50p. To get there SDC had to devise a new workflow in order to work with Sony’s latest SRMaster format. This included ingesting 4K 50P material from SR-R1000 decks and encoding using a new beta version of DVS Clipster programmed especially for this project.
SDC, Sony and NT Live successfully tested a 4K DCP from Sony's SRMaster, which is currently confirmed to work with Sony’s SRX-R320 4K projectors.
In the UK, approximately 500 screens showed War Horse live with many also showing a delayed version; in the US around 300 screens took the live feed and another 100 showed delayed; Canada featured 100 showings; Europe about 80 and in the rest of the world including Australia, Russia, Mexico, and Japan there were 80 delayed shows.
The technical set up is very similar to that of a 4K sports OB. In fact Andy Hotten, Sony's technical project manager, was in Turkey the week before War Horse overseeing a 4K production for Turkish satellite broadcaster Digiturk of a Galatasaray and Besiktas match in which four F55s and two upconverted HDcams were fed through a MVS-8000X and linked back to a hotel for a VIP screening.
“After War Horse we will have established a proven workflow for 24p 4K distribution with an option for cinemas to take it to 50p 4K,” said Bretnall. “We know that many cinemas are capable of showing 4K and we know a small number are capable of showing it live with few additional high hurdles than for the last 35 NT Live productions.”
By Adrian Pennington