[opendtv] Re: MPEG-2 et al
- From: Tom Barry <trbarry@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Mon, 24 Jan 2005 08:04:00 -0500
Tom McMahon wrote:
> H.264/AVC was designed to serve many masters and the test cases were
explicitly manifold (in contrast to the above). I think we did
> a pretty good job of bashing the mathematical concepts against a
severe range of representative market-based content during the
> development process. That is why we're seeing 1) such good coding
results and 2) why H.264/AVC will only get that much better as
> ENcoder manufacturers better-employ the range of tools we've built
into the standard.
>
Well, the Nero AVC codec already appears to be winning in the most
recent www.doom9.net (DVD rippers board) codec shoot out as implemented.
But is it possible with the AVC design to reduce the resolution without
re-encoding as I was discussing, for transmission, stat-mux, etc? This
does not seem to have been a priority in the design and yet might be
very valuable commercially where video it must be encoded once and
delivered at various rates.
- Tom
> One thing I've come to appreciate over the years is that the output quality
> of a video codec standards body is only as good as the
> test content that it uses to develop the respective standard, and only then
> across the range of resolutions and bitrates that were
> used in the development process.
>
> In any of these activities, there are numerous proposals on how to tweak and
> tune the "design" for greater efficiency and/or
> quality. Proposals are accepted into the standard or rejected based on the
> numbers and an ability to have some else reproduce your
> results. However, sometimes the proposed algorithms (or "tools") are highly
> content dependent (or only work at higher bitrate, for
> example). That which shows great results for interlace may not work well for
> film grain. And so on.
>
> In the development of MPEG-2 people were groping in the dark in this respect.
> When MPEG-2 was developed there was no digital cable,
> there was no digital satellite, there were no DVDs, there was no HD. The
> content used to develop and tweak the Standard was ad hoc
> at best.
>
> H.264/AVC was designed to serve many masters and the test cases were
> explicitly manifold (in contrast to the above). I think we did
> a pretty good job of bashing the mathematical concepts against a severe range
> of representative market-based content during the
> development process. That is why we're seeing 1) such good coding results and
> 2) why H.264/AVC will only get that much better as
> ENcoder manufacturers better-employ the range of tools we've built into the
> standard.
>
> -----Original Message-----
> From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] On
> Behalf Of Tom Barry
> Sent: Sunday, January 23, 2005 4:17 PM
>
> Manfredi, Albert E wrote:
>
> > Can't you do that already with MPEG-2? For > example, isn't that exactly
> what happens when > MPEG-2 is used in a fixed bit rate
> mode? You > get variable quality.
>
> I think you get variable quality but only by decreasing the precision of each
> frequency component of a block, not by decreasing the
> resolution and total number of blocks sent. For instance, if you send 720p in
> MPEG2 at only 5-6 megabits it will likely look worse than if you instead
> scaled it down to 480 lines (or less) and scaled it back up
> for display.
> It seems there is sort of a sweet spot resolution for each source and bit
> rate. So it is probably better to vary both the
> quantization and resolution IMHO.
>
> - Tom
>
>
>
>>Tom Barry wrote:
>>
>>
>>
>>>Thus I'd predict we eventually will have
>>>compressed video that has a MAX resolution
>>>but not a fixed one and we can then just
>>>rate shape everything from a single source
>>>to multiple targets such as sub-channels
>>>and cell phones. Each step along the way
>>>might discard a bit more as needed. But
>>>the master archives would be pre-encoded at
>>>highest quality
>>
>>
>>Can't you do that already with MPEG-2? For
>>example, isn't that exactly what happens when
>>MPEG-2 is used in a fixed bit rate mode? You
>>get variable quality.
>>
>>Bert
>>
>>
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