I also notice in the FAQ section they will be transmitting in 720p, which is interesting. I guess there are many more 720p capable sets in the market than 1080p, which makes sense, and I also guess the bandwidth is less than full 1920x1080p.
Could someone explain the 2nd to last comment at bitrates, especially the mutiplexing part? Does it mean they will have 2HD and 3SD channels sharing a 23Mbit stream?
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Comment by cyril7, on 28-Sep-2007 10:30
Hi Tim, DVB-T maxs out at around 23Mb/s of usable throughput (ie post FEC) it all depends on what modulation and number of cofdm carriers (2k or 8k), but 23Mb/s is full chat. This compares to around 30Mb/s usable post FEC bitrate on the current DVB-S muxs that FreeView and Sky uses. I expect Sky will use DVB-S2 when it puts a HD mux in, this would render around 42-45Mb/s out of the same transponder bandwidth as the currrent muxs.
So 23Mb/s for two 720p streams and a couple of 576i ones is a bit tight I think. Interesting that they have gone for 720p, makes sense really as all current domestic HD displays are panel displays that are progressive, and the biggest weakpoint of domestic displays is the deinterlacer. So as most HD material that broadcasters produce and get is 1080i. Having the broadcaster do the deinterlacing and scaling to the most common 720
using a broadcast quality deinterlacer/scaler makes good sense and removes major limitation between cheaper and more expensive panels displays. The BBC have made a lot of this aspect of recent times.
I would expect with mpeg4 a couple of 720p streams would want 8-10Mb/s each, doesnt leave much room for the two SD channels.
Comment by openmedia, on 28-Sep-2007 11:14
Yes they will be showing a total of 5 channels in their 23Mbit multiplex.
As Sport Extra isn't 24/7 i'd expect split an average 8+8+2+2+2 with room to move bandwidth around from Sport Extra when off air.
Comment by sbiddle, on 28-Sep-2007 12:22
Broadcasting full 1080p just isn't isn't feasible. Hardly anybody is doing it simply because of the bandwidth requirements.
There is also the arguement that for anything less than a 50" screen that the difference between 720p and 1080p isn't noticeable and worth factoring in as well is the rather large issue of very few sets that are actually full HD. Virtually all TV's will handle 1080p input these days but feeding 1080p into a screen that's only 1366x768 is rather pointless - you may as well just feed it 720p.
Comment by Kunal Narsey, on 28-Sep-2007 15:27
Yes, they will all be sharing the streaming bandwidth..
Comment by macuser, on 28-Sep-2007 21:55
I don't really think the alturnative was ever 1080p, but 1080i, which is a whole different thing intirely(shows 540 lines of resolution at one moment instead of 1080). The only problem is that 720p is not supported by most early CRT HD displays, meaning that they are either going to have to downscale to 480i/p or not watch the channel at all(does the set-top box have a scaler inbuilt?)
Anyway, I can't wait!
Comment by John Sayers, on 19-Oct-2008 09:14
I can not find any information about where to direct the antenna for HD transmission. In Auckland is it the Sky Tower or Waitakeri?