Recent work on specification has focused on the SMPTE specification
for Dirac Pro/VC-2. VC-2 or SMPTE 2042 is the intraframe coding
subset of the complete Dirac spec. Although that may sound like a
small sub-set, in fact it includes most of the Dirac spec. It
includes everything about the wavelet transform and arithmetic
coding, data types, stream syntax etc. Of course it doesn't include
details of the inter frame coding but that actually represents a
relatively small proportion of the spec.
I have been working with the SMPTE on specification over the past few
years. Late last year the core part of the Dirac Pro spec SMPTE
2042-1 was ratified. This is a one hundred and thirty odd page spec
defining the core decoder. More recently parts 2 (level
specifications) and part 3 (conformance testing, including
conformance test streams) have also been ratified. So now Dirac
Pro/VC-2/SMPTE 2042 is a fully ratified international codec spec
available from the SMPTE store. In addition there are some
specialised SMPTE specs relating to specific broadcast applications.
In considering updating the Dirac long GOP spec we need to ensure
that the SMPTE spec remains the master (as far as it goes). It would
be bad if the two specifications diverged. The SMPTE spec has been
subject to considerable peer review in the SMPTE standards committee.
It has diverged from the Dirac spec in order to correct bugs etc. It
is a more reliable reference for the part of Dirac that it covers
than the Dirac spec. Of course, like all documents, it probably still
has bugs in it. I would request that if Dirac users have queries
about the Dirac spec they first check the SMPTE spec. If they could
then note and send me any errors I can get them corrigendum to the
specification. If you aren't able to obtain a copy of the SMPTE spec
then contact me and I will see what I can do.
I think the long GOP Dirac spec needs redrafting so that it
normatively includes the SMPTE spec by reference. That way we can
ensure that the two do not diverge. This is quite a lot of work and,
at present, the BBC is reluctant to commit many resources, but I will
see what I can do. Ideally we would release an addition to the
existing specification (SMPTE 2042 part 4?) that includes the
interframe coding specification. This is possible but, having worked
on the VC-2 spec or several years, I know that it is a lot of work.
Anyone out there willing to help?
Please get back to me on issues of specification and standardisation.
Best regards
Tim Borer
At 06:50 05/03/2010, Tommy Thorn wrote:
[resent as I accidentally didn't reply-all]
On Thu, Mar 4, 2010 at 2:43 AM, Thomas Davies
<<mailto:thomas.dav...@bbc.co.uk>thomas.dav...@bbc.co.uk> wrote:
The BBC isn't actively working on the code-bases anymore, since it's
"out in the wild".
Thanks for the update Thomas, but what about the spec? The 2.2.3
draft has a number of issues, including outright bugs. I went
looking for the latex source to propose patches, but I could only
find version 2.2.1 in the CVS repository. Sadly, the more recent git
repository doesn't appear to have the latex sources for the spec.
Cheers
Tommy
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