[opendtv] Re: News: Intel introduces chips designed to improve Internet video quality
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Tue, 20 Nov 2007 14:24:21 -0500
At 12:40 PM -0500 11/20/07, Tom Barry wrote:
Anybody know if AVC-intra still has much advantage over MPEG-2 if it
is using just intra-frame compression and loses the advantages of
its fancier (and CPU intensive) motion compensation modes?
The only "advantage" of interframe compression is the ability to
achieve much higher compression ratios than are possible with
intraframe compression. This is obviously important for emission
coding. IMHO the use of interframe coding has been misapplied for
field acquisition and production. The entire non-linear editing
revolution has been possible in large measure because there has been
sufficient storage to deal with compressing every frame using
intraframe techniques. This allows each frame to be stored with the
same level of quality and virtually instant random access to any
frame. The processing resources needed to work with these frames are
essentially symetrical and far less demanding than those needed to
handle real time motion compensated prediction.
With an interframe codec like MPEG-2 we gain compression efficiency
at the expense of compression complexity. We need far more processing
resources to handle the encoding, we lose more information, and we
may introduce artifacts in the process. In order to access ANY frame
we must decode a GOP, which take longer; worse yet, the amount of
information in B-frames is lower than for I and P frames.
The emergence of interframe codecs for image acquisition is based
almost entirely on the need to reduce the bit rate to take advantage
of legacy storage techniques - HDV uses the same tape transports and
bit rates as DV, which is an intraframe codec. But it relies on
MPEG-2 to selectively throw away more information; this works fairly
well if the source image is progressive (i.e 1280 x 720 @ 24/60P),
but not as well for 1080i when there is rapid motion.
Panasonic has demonstrated the improvement in quality of AVC intra
over the older DVC Pro codecs. The key is the ability to capture at
50 or 100 Mbps. IMHO this is much easier to justify than using an
interframe codec at lower bit rates.
Interframe coding should be reserved for application where bandwidth
more valuable than computer storage and processing resources, which
now handle both intraframe compressed and UNCOMPRESSED HDTV images
without much strain.
Regards
Craig
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