Half Frame Width HD Video Backhaul

Yep - I was clear to use the word platforms and never suggested that HD Lite was used for ATSC platforms (though ATSC QAM cable operators do resolution conversion, and some affiliates of '1080i' networks broadcast at 720p on their ATSC 8VSB OTA transmissions I believe - some PBS stations for example)

HD Lite was particularly a thing for satellite operators who had to cope with large numbers of local regional affiliates on their platform, and didn't have the bandwidth to carry them - and all the other national channels - at full quality. HD Lite was their solution to getting bitrates down...



Yep - HD Lite was (and may still be) more of a satellite thing.

In the days when DVC Pro HD and HD Cam (1280x1080 and 1440x1080 respectively at i29.97) were often used in acquisition - there often wasn't much information between 1280 and 1920 horizontally anyway... However once HD Cam SR, XD Cam 422 HD etc. became widespread (and for operators using HD-D5 back in the day instead of HD Cam) there was good reason to keep to 1920. (DVC Pro HD in 720p is even worse - it's 960x720 at p59.94)

I guess that's quite a neat solution to send two feeds back to the studio with the same latency.

Or possibly a cheap way of providing a back up for two separate feeds.

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?

BT and others send 4 * 1920 * 1080 HD pictures, which are multiplexed together for broadcast as one single 3840 * 2160 at the broadcast HQ .

I think two things have got conflated here.
You can send UHD as four 1080p quadrants encoded with H264 in one mux - but it's not very efficient in terms of equipment or bandwidth, and risks your four decoders not quite decoding in sync - so you get a quadrant out.

This is being depreciated in favour of using H265 encoders to send a single 2160p raster.

You can also use H265 to send four individual cameras as if it were a single 2160p image (essentially a quad split), and use it in a remote production scenario, producing an HD programme - thus using fewer encoders and satellite space than using one per camera.

And the quad split approach ensures the 4 feeds do stay in sync.

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)

I thought you were saying that the MVPD were changing the resolutions of OTA channels. Which is something that as far as I know they are not allowed to do either both by contract or by law (I think both).

Affiliates typically have to follow the network resolutions however if a station has secondary affiliate (or sometimes three) major network affiliations the contract allows the station to down convert the resolution. Typically down to 720p and there's a often a clause in the affiliation contracts that usually says that the station must if they have the technology to broadcast at its required resolution. Additionally if the station feeds to the MVPD headend they typically require the station to transmit the networks standard resolution to the headend.

Here's an interesting list of stations that cross convert the network's standard resolution.

But we got off track. Thanks for the information.