[x264-devel] Re: Error Concealment

[Ryan Dalzell]

On Wednesday 17 January 2007 16:42, List, Peter wrote:
> > > > This gets even worse when slices can be out of order across
> picture
> > > > boundaries. I have searched high and low the spec and I cannot
> find a
> > > > statement that precludes this from happening. (Of course, due to
> the
> > > > lack
> > > > of plain English in the spec it could be there.)
> > >
> > > I will check if that is possible, but I definitely do not believe it
> is!
>
> > > And yes, this standard is not that easy to read :-)
> >
> > Please do check as I would love to be proven wrong on this one.
>
> What about paragraph 7.4.1.2.3 (I LOOOVE documents with 5 level nesting)
>
> 7.4.1.2.3   Order of NAL units and coded pictures and association to
> access units
>
>
> An access unit consists of one primary coded picture, zero or more
> corresponding redundant coded pictures, and zero or more non-VCL NAL
> units. The association of VCL NAL units to primary or redundant coded
> pictures is described in subclause 7.4.1.2.5.
>
> The first access unit in the bitstream starts with the first NAL unit of
> the bitstream.
>
> The first of any of the following NAL units after the last VCL NAL unit
> of a primary coded picture specifies the start of a new access unit.
>
> -         access unit delimiter NAL unit (when present)
>
> -         sequence parameter set NAL unit (when present)
>
> -         picture parameter set NAL unit (when present)
>
> -         SEI NAL unit (when present)
>
> -         NAL units with nal_unit_type in the range of 14 to 18,
> inclusive
>
> -         first VCL NAL unit of a primary coded picture (always present)
>
> I think this should prove that access units can not be mixed. It's hard
> to be sure though...

I saw your your question on jvt-experts. And if Gary says that ASO across 
picture boundaries is prohibited then I am delighted. However I have 
re-read all of 7.4.2.1 and I fail to see how the language in the subclause 
prohibits this. It all depends on your definition of an "access unit" I 
suppose. I have followed this up on th jvt-experts as I am sure you will 
see.

Anyway, you learn something new every day, and sometimes it's really good 
news! Thanks for following this up.

Cheers,
-Ryan

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