[opendtv] Re: Food for thought

At 1:17 PM -0500 2/21/07, Manfredi, Albert E wrote:

As it is, no one should pretend that it's H.264 or bust. It simply is
not borne out by the facts. Neither the US nor the Aussie versions of
HDTV are heavily compromised by their use of H.262, until some future
codec comes along.


Now Bert is an expert viewer down under as well.

Hmmmm... maybe this explains where his head is at.
;-)
The situation in both the U.S. and Australia is similar. HD encoded using MPEG-2 needs all of the available bits, and still exhibits significaint artifacts when the peak bit rate requirement exceeds the channel capacity. When HD is multiplexed with HD something has to give, and its delivered image quality.
Just for grins I typed HD bitrates for Australian DTV into Google.So what do you think I found Bert? Glowing reports of how good it is? 

NO BERT. Complaints about how compromised the service is:

Here's just one of many examples

http://www.dtvforum.info/lofiversion/index.php/t10231.html


Champion_R
Oct 26 2004, 05:08 PM
What do Sydney HD viewers think of their HD being cut down by .5mbits to boost SD by .5mbits? Nine HD Sydney is now Australia's lowest bitrate 1080i channel. I think it's stupid taking bandwidth from an already starved channel to prop up a channel that already has ample bandwidth. Joe Average and their 4:3 TV can't even resolve the full resolution of SD so why are we wasting bandwidth on people who won't see any benefit but HD viewers will suffer dearly with the woeful bitrate of 11.8mbits.
I think SD should be a maximum of 5mbits on all channels and HD channels should upconvert SD content so people with better displays get a better signal and people with 4:3 CRTs wouldn't notice a thing. Retailers should be provided with a demo loop playing off DVHS or they can be stored on and played off a Satallite.
Just before I go, here's a rough draft of a graph showing the bitrates of channels in most capital cities. http://img100.exs.cx/img100/5839/DVBBitrates.gif, how much do you get shafted by your broadcasters?
But wait Bert. This must just be some of those complainers who like to post on e-mail reflectors. Surely the government would not create a lose-lose situation...Right? 

www.dba.org.au/uploads/documents/CJKnowlesABS2003.pdf

Impact of HDTV Transmission of DTV Multi-Channel Broadcasting
paper delivered to
Australian Broadcasting Summit
Sydney Australia February 2003
by
Colin J Knowles
Director Technology and Distribution
Australian Broadcasting Corporation
In Australia, the legislation mandated that broadcasters transmit on the digital channel both an SDTV and HDTV image simultaneously whenever HDTV was transmitted. This provision was designed to ensure early availability of set-top-boxes in the market place, but it has created a legacy problem for broadcasters. The promise of a variety of cheap set-top-boxes, and receivers was not delivered, and it did not take too long before STBs appeared, which did not need a simulcast SDTV transmission to address the needs of standard definition display devices.
However, for the moment, the obligation remains, and it places a number of constraints on broadcasters. A 7 MHz wide television channel can transmit around 20 Mbit/s of data. We need to use around 6 Mbit/s to deliver a digital SDTV signal that is in quality terms equivalent to analog reception under good conditions. At this level the signal will look better than analog for many viewers because of the digital signal's stronger immunity to disturbances like ghosting, and for all viewers, even those in the best analog viewing situations, the digital signal will not look worse than analog. For certain types of content, lower bit-rates may be used. In the free-to-air environment, where we have a mix of live, pre-recorded and film sourced material that is generally shown once only, lower bitrates are difficult to achieve without considerable additional cost. It is more practical to strike a bit-rate that meets most needs and stick with it, rather than constantly adjust the rate to suit the material. Techniques such as statistical multiplexing can do this virtually automatically, but generally they need a number of independent programs (4 or more) with several different types of content sharing a common transmission channel to show useful gains. At this point in time, the available channel and content options show little benefit from this additional complexity.
An HDTV channel at the time the standard was established needed at least 19 Mbit/s for most material. Given some improvements in encoding a practical minimum for true HDTV transmission lies between 12 and 15 Mbit/s for the picture, depending on the type of material (e.g. film vs fast live action sport). If we take these requirements together with the simulcast requirement, plus sound and basic data such as system information, the transmission of HDTV with its SDTV equivalent is a compromise. Together they consume all of the available bandwidth.
Bottom line Bert, using MPEG-2, any combination of SD and HD requires the image quality to be compromised. Using h.264 the quality will be LESS compromised. 


So tell me something I don't know.


There's not enough time Bert.


Once again, had they claimed that
each SD program can be replaced at the same bit rate by an HD program,
the value of H.264 would have been undisputable.
Funny. You find immense value in the incremental improvements in 8VSB receiver technology over the past decade, and boldly claim that mobile ATSC is just around the corner. But you cannot understand that the same thing is happening with encoding technology.
MPEG-2 encoders evolved for nearly a decade before they essentially hit the wall in terms of further improvements. H.264 significantly enhances the tool available to improve video encoding, at the expense of many more MIPs of computing power. We are just at the beginning of the "exploitation curve" for h.264, and it is ALREADY showing major gains over MPEG-2 on the order of 15-25% for high quality video delivery (more for bandwidth limited applications like mobile).
What's more, h.264 will be fully exploited and a replacement will be in the wings in 5-7 years. Such is the nature of the digital wave we are riding. 


Every change in a deployed standard comes at a price. If you have to
pick a time when an upgrade is to be implemented, you're better off
making sure the upgrade is an obvious improvement. In the case of the
BBC, introducing HDTV in a market with no HDTV and no deployed MPEG-2 MP
at HL boxes at all, it's no big shakes to go to H.264. In countries
where HDTV is deployed and working just fine, I would wait until
something more efficient comes along.
You mean like the difference between multichannel services with hundreds of channels versus a dying broadcast model with 5-10 programs per market? 

Regards
Craig


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