I don’t understand if BT are sending quad feeds in UHD for 4hd pictures does that mean bt aren’t broadcasting true UHD pictures?
No - it's perfectly routine to produce in Quad HD and until 2160p50 h.265 broadcast encoders and decoders were widespread, 4 x 1920x1080p50 h.264 streams were sometimes backhauled over fibre or satellite. You have to work very hard to ensure the 4 streams say in sync with each other - otherwise you will see 1/4 of the picture cut early/late compared to the others for instance.
You effectively send a single UHD picture as 4 x HD streams (1080p50 not 1080i25)
Also - in UHD production almost no studios or OB trucks use 2160p50 12G-SDI for interconnects, they either use Quad 2022-6/7 (3G-SDI 1920x1080 over IP) or 2110 (2160p50 or Quad 1080p50 elementary streams over IP), or Quad 3G-SDI (4 x 1920x1080p50 in either Quadrant or 2SI modes) In fact a lot of vision mixers and servers like EVS were upgraded to UHD with relatively few modifications (they took in one UHD signal via 4 HD inputs, and output one UHD signal as 4 HD outputs - you quartered the number of inputs and outputs - but didn't have to totally re-engineer your product...)
1920 x 2= 3840
1080 x 2 = 1080
So 4 x 1080p50 streams = 1x 2160p50 - and if you keep them all in sync you're fine.
In Quad 3G-SDI - Quadrant mode splits the picture into 4 quarters, 2SI mode switches the feeds in small groups of pixels (it isn't 2x2 pixels but that's a good way of thinking about it) so with 2SI you get 4 x full size 16:9 pictures (rather than quarter screen portions) (Ironically this was what the BBC and Phiips/BTS did in the late 80s when they recorded 1440x1152 Eureka 1250 HD as 4 x SD 720x576 digital streams onto D1 VTRs. What goes around comes around - the BBC system was very similar to 2SI, the Phiilps/BTS system was Quadrant)
HOWEVER - as thegeek mentioned - h.265 2160p50 encoders are now available and so you can backhaul a UHD video stream (whether produced in Quad 3G or 2160p50 native) as a single stream. As a by product - if you are doing HD remote production (i.e. not UHD) you can backhaul 4 camera outputs (for cutting back at base rather than on-site, or multiple event streams) as 4 x 1080p50 streams as a Quad Split in 1 x 2160p50 stream, rather than backhauling 4 x 1080p50 h.264 or h.265 streams - and by keeping them as a single 2160p50 stream you have everything nice and in sync (particularly relevant for remote camera feeds)
Last edited by noggin on 12 November 2019 11:32am - 2 times in total
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