Re: [Cellar] I-D Action: draft-ietf-cellar-ffv1-15.txt

"Murray S. Kucherawy" <superuser@gmail.com> Thu, 25 June 2020 17:32 UTC

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From: "Murray S. Kucherawy" <superuser@gmail.com>
Date: Thu, 25 Jun 2020 10:31:46 -0700
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To: Jerome Martinez <jerome@mediaarea.net>
Cc: Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com>, Codec Encoding for LossLess Archiving and Realtime transmission <cellar@ietf.org>
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Subject: Re: [Cellar] I-D Action: draft-ietf-cellar-ffv1-15.txt
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On Thu, Jun 25, 2020 at 10:19 AM Jerome Martinez <jerome@mediaarea.net>
wrote:

> On 25/06/2020 18:24, Murray S. Kucherawy wrote:
>
> Hooray, most of those "type" columns are gone!  But, alas, not all of
> them.  They're still present in Sections 4.1 and below.  I counted at least
> seven of them just in the diff I'm reviewing.  As before, they should also
> be removed, or at least explained.
>
> A minor point: Prior to Section 3.8.2.3, it looks like all of the examples
> are in C.  After that, they switch to pseudo code.  Any reason we can't be
> consistent?
>
> The figures before section 4 are autonomous functions, used for describing
> a part of the algorithm and not used for directly reading out any symbol
> from the bitstream, so it was making sense to remove the "type" column at
> these places (this column was not used there). They could be more
> pseudocode nonetheless, as the C types ("int" etc) are not really relevant
> (they depends on the programming language).
>
> The figures in section 4 are for explaining the bitstream parsing order,
> and the "type" column is used for indicating the kind of value it is (types
> are described in
> https://tools.ietf.org/id/draft-ietf-cellar-ffv1-15.html#table-4 , I see
> that it is called "Symbol" here, we'll change "Symbol" to "Type" in this
> table).
> This kind of method for describing a video bitstream is very classic, for
> example in:
> - H.264, see the full spec (PDF to download)
> https://www.itu.int/rec/T-REC-H.264-201906-I/en
> - AV1, see an online direct example at
> https://aomediacodec.github.io/av1-spec/#frame-obu-syntax
>
> As in theses specs, we have some figures without usage of the "type"
> column because they are intermediate figures (the "type" column is used in
> the figures using this figure and the figures called by this figure), split
> from another figure, in order to have the spec more readable (focusing on a
> specific topic). AV1 uses it for example at
> https://aomediacodec.github.io/av1-spec/#decode-tile-syntax
>

Your previous AD and I were both confused by the format and what it's
trying to convey.  I appreciate that it might be classic in some realms,
but as neither of us had seen it, I imagine others on the IESG who don't
work in our layers (i.e., most of them) will also ask about it.  If you
want to leave them in, I suggest including either some text about how to
interpret them, or a reference to such guidance elsewhere.

-MSK