[opendtv] Re: (no subject)
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 11 Dec 2009 08:21:35 -0500
At 10:16 AM -0600 12/10/09, Manfredi, Albert E wrote:
Craig Birkmaier wrote:
MPEG-2 defines both the transport stream (TS) and an image compression
algorithm. The image compression algorithm is the same one that the
ITU calls "H.262."
Not Exactly!
Just quibbling with this part of your post, Craig.
Yes exactly. Part 2 of MPEG-2 defines the video compression
algorithm. It only describes one: the algorithm that the ITU
identifies as H.262.
Really?
This is part 2 of the h.262 standard
2 Normative references
The following ITU-T Recommendations and International Standards
contain provisions which through reference in this text, constitute
provisions of this Recommendation | International Standard. At the
time of publication, the editions indicated were valid. All
Recommendations and Standards are subject to revision, and parties to
agreements based on this Recommendation | International Standard are
encouraged to investigate the possibility of applying the most recent
editions of the standards indicated below. Members of IEC and ISO
maintain registers of currently valid International Standards. The
Telecommunication Standardisation Bureau maintains a list of
currently valid ITU-T Recommendations.
It then lists the references, including MPEG-1. There are no
references to a video compress algorithm.
Then in section 3 - definitions we find:
3.50 encoding (process): A process, not specified in this
specification, that reads a stream of
input pictures or audio samples and produces a valid coded bitstream
as defined in this
specification.
Clearly, defining the tools and the syntax for a coded bitstream does
help to define the encoder, but it does not limit innovation in how
the encoding process can be implemented. For example, you can use the
very crude block matching functions described in the standard to
produce motion vectors, or you could use very sophisticated motion
compensated prediction to determine what is moving and where, then
use this information to select the blocks that the decoder will use
to build its reference frames and the motion vectors needed to
complete the prediction.
And once again, there is no definition of an algorithm ANYWHERE in
the standard, only the tools that are available and the syntax for
the decoder to reconstruct the image streams.
Regards
Craig
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