[opendtv] Re: MPEG-2 et al
- From: Ron Economos <k6mpg@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 25 Jan 2005 02:59:54 -0800
When a civilization far in the future digs up the ruins
of our civilization, I'm sure they will find a clip of
"Mobile and Calender". ;)
Ron
Tom McMahon wrote:
>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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