adl ch7 is broadcasting real HD res (even if upscaled) unlike ch10

chopper · June 08, 2009, 10:27:25 AM

What happened ? I'd thought adelaide channel 7 was broadcasting pretend HD (1440x1080i) like channel 10 "HD" but a check today indicated it was 1920x1080i (not sure of the sustained bitrates though, and it's a trade-off as you know).

tonymy01 · June 08, 2009, 11:20:10 AM

What 10HD? Since OneHD came along, there is no 10HD any more. If your STB indicates 10HD then you have a problem (perhaps you need to clear your channels and rescan). Or are you in a regional area where OneHD hasn't come long (and then it isn't really TenHD, it is Southern X)?
1440x1080 is in no way "pretend" HD. It is actually quite sufficient to broadcast real HD material with very little degradation compared to 1920x1080. In fact, the quality is typically better, as there are less pixels to compress so less compression artefacts at the low bitrates that they are stuck with in a 3xMPEG2 channel per mux environment.
And looking at the received resolution is in no way an indicator of the actual resolution of the show being watched. You will find *all* broadcasters (including OneHD) is still upscaling a heap of material for their HD channel. So the ICEguide for any shows that mirror the SD channel and are only upscaled versions of the SD channel will not show any guide for those shows, e.g. ABCHD (which only has a handful of real HD shows per week on their HD channel).

chopper · June 08, 2009, 07:30:03 PM

Quote from: tonymy01 on June 08, 2009, 11:20:10 AM
What 10HD? Since OneHD came along, there is no 10HD any more. ... 1440x1080 is in no way "pretend" HD. It is actually quite sufficient to broadcast real HD material with very little degradation compared to 1920x1080. In fact, the quality is typically better, as there are less pixels to compress so less compression artefacts at the low bitrates that they are stuck with in a 3xMPEG2 channel per mux environment.
And looking at the received resolution is in no way an indicator of the actual resolution of the show being watched.

OK, One HD. i understand the bitrate mux constraint and wish it wasn't there. 7 and 9 seem to only have 2 channels per mux and appear to have 1920x1080i at higher bitrates than one "HD" ? hence "better" picture for the true HD stuff (1440 is only 75% of the true HD's pixels).

I'd thought 7 and/or 9 had gone to 1440 too but apparently not.

prl · June 08, 2009, 08:14:33 PM

Quote from: chopper on June 08, 2009, 07:30:03 PM...
OK, One HD. i understand the bitrate mux constraint and wish it wasn't there.
...

Welcome to the world of physics and information theory, in particular the Shannon-Hartley theorem, the "there's no such thing as a free lunch" theorem about noise and channel bitrate. :)

chopper · June 08, 2009, 09:30:04 PM

:) Yep no free lunch. And I spotted a 1440 from 9 just today (as well as a 1920 last night), so I don't know if they're chopping and changing or what.

They COULD decide to stay with 2 channels per mux and not 3 like ONE and therefore broadcast @ 1920x1080i with a higher bitrate ... but heY FREEVIEW kills that (and therefore nice HD btw) doesn't it ? More channels has to be better, according to freeview, hey ! Never mind the quality, feel the width.

tonymy01 · June 08, 2009, 10:23:01 PM

OneHD is broadcast at a pretty good bitrate. They use stat-muxing these days, so the bitrate is variable, but up towards 16megabit/s (which is why One digital and Ten digital are looking so lousy lately, they have to fight over the remaining 6megabit/s when OneHD peaks). You will find Nein and Seven would be lucky to be 13 or 14.5megabit/s for their HD (with approx 7.5megabit/s for the SD channel remaining).
So 1440x1080 of various HD channels can still take a high bitrate, but looks better than using the same methods for 1920x1080. Even on a trueHD screen you would be extremely hard pressed to be able to spot any difference in having the 1920 knocked back to 1440 resolution wise. But you would certainly notice chunky blocks on a bit starved 1920x1080 broadcast.

prl · June 09, 2009, 09:43:54 AM

I can't recall whether it was discussed on the IceTV forum, but I and some other posters on the Beyonwiz and DTV forums have been posting about the two big potential quality problems with Freeview pretty much since it was announced - the fact that squeezing another channel into a fixed bit bandwidth budget was always going to cause problems with picture quality, and the fact that there didn't seem to be any clear funding model to pay for content on the extra channels, especially on the commercial channels, so content quality was also likely to suffer.

chopper · June 09, 2009, 09:18:08 PM

yes I saw them and probably posted there too. i was wondering if the channels chop and change their resolutions. stat muxing isn't magic, if all want high bitrates which you'd expect of video, then something has to give and what gives depends on allocated priorities and base rates - you do not get something for nothing. i'd like to see sets of figures on the "high" ONE bitrates as i suspect it doesn't really happen in practice. 3 into 2 doesn't go. i suspect 2 into 2 probably goes better for both, but the different resolutions throw me a bit on that question.