[opendtv] Re: Video compression artifacts and MPEG noise reduction
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 24 Jun 2008 18:09:39 -0400
Craig Birkmaier wrote:
> One thing is clear from the presentations, h.264 with the FRE
> is significantly more efficient than MPEG-2 ( 8 mbps for h.264
> versus 24 mbps for h.262 for essentially the same level of
> perceived quality.)
Honestly, though, isn't there some bone in your body that questions
these assertions, even after real world experience has shown that things
aren't quite so cut and dried?
I saw that same presentation, and all I could conclude is that the
comparison was probably valid for A PARTICULAR MPEG-2 encoding. Or
perhaps, for some odd reason, the result only applied to a very specific
case of compressing 1080 at 24p material. So I did a little searching.
One interesting tid bit I found was that MPEG-2 encoding can be much
more effective if the composition of the GOP is varied in real time,
according to the subject matter. And that decoders can handle this
variation quite nicely.
Another interesting discovery was an explanation of the AVC deblocking
filter. Seems like a completely separate algorithm within AVC, which can
just as easily be applied to MPEG-2, or any other block-based algorithm,
as it can be to AVC. (Very likely what Algolith did.)
Another interesting and not-too-recent improvement was this Digigami
system:
http://www.engadgethd.com/2005/12/23/rumors-of-mpeg-2s-death-greatly-exa
ggerated-digigami-does-hd-o/
from end of 2005. Which claims that 720p can be compressed in MPEG-2
down to 3 - 7 Mb/s. I assume this means 720 at 24p, presumably DVD
movies. Still, that easily meets the 50 percent improvement over the
normal MPEG-2 rates we have seen quoted to us over the past decade.
(Wasn't 720 at 24p supposed to require an average of 9 to 10 Mb/s in
MPEG-2? Isn't an average of ~5 Mb/s a 50 percent improvement?)
So if the 1080 at 24p file in the presentation was encoded using this
process, would it still require 24 Mb/s for equal quality to the AVC
file at 8 Mb/s? I'll bet you it would not. My bet is that the comparison
would have been far less dramatic if state of the art MPEG-2 techniques
had been used.
There are plenty of articles online that repeat the party line. There
are other articles which present a much more balanced picture of the
codec wars, such as this recent one:
http://www.studiodaily.com/studiomonthly/currentissue/9262.html
Unless we own IP in AVC, I'm not sure what motivates the constant
exaggeration of the facts. I don't think MPEG-2 encoding is hopeless
just yet. I do think that the comparisons made against MPEG-2 are VERY
often biased, and for obvious reasons. Meanwhile, for systems where
migration to AVC is painful, there seems to be NO EXCUSE for this
pretense that we can't move on without it.
Bert
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