[FFmpeg-devel] [PATCH] Implement PAFF in H.264

[Martin Zlomek]

On Fri, 21 Sep 2007 18:06:32 +0200, Jeff Downs <heydowns at borg.com> wrote:

> On Thu, 20 Sep 2007, Martin Zlomek wrote:
>
>> The attached patch fixes CurrPicNum of short term reference  
>> fields/frames
>> in reference picture list reordering.
>>
>> --- h264.c.orig	2007-09-20 23:30:38.000000000 +0200
>> +++ h264.c	2007-09-20 23:30:53.000000000 +0200
>> @@ -3056,6 +3056,9 @@
>>                              add = 0;
>>                          }
>>
>> +                        if (pred > h->curr_pic_num)
>> +                            pred -= h->max_pic_num;
>> +
>>                          for(i= h->short_ref_count-1; i>=0; i--){
>>                              ref = h->short_ref[i];
>>                              assert(ref->reference == 3);
>
> This doesn't look right -- shouldn't the wrap check come prior to the
> block at the start of the patch? At this point of insertion, frame number
> to look for has already been determined.  Also, pred value can't be
> modified like this; it can be used in subsequent iterations of the loop
> and has to retain the unmodified value.
>
> This is actually not intimately tied to PAFF support; this was there all
> along so I'm guessing this should be kept distinct from the PAFF support
> patches.
>
> So, the attached patch is one more to add, to be applied after the
> PAFF patches.  A different (smaller) patch is needed if we want to fix
> prior to PAFF.
>
> 	-Jeff

It seems that it is wrong, but it is not really true.
You are right that I have applied formula 8-37 in "8.2.4.3.1 Reordering
process of reference picture lists for short-term reference pictures"
section of h.264 spec in a wrong way, but it is "fixed" in each
following loop of the for-cycle by line

   pred &= h->max_pic_num - 1;

Anyway, my previously posted patch should be replaced by the attached
one; it has the same effect but looks better.

For my tests, I use the following sample and the results are better
with the patch:
http://ftp3.itu.ch/av-arch/jvt-site/draft_conformance/MR6_BT_B.zip


-- 
Martin Zlomek
martin.zlomek at email.cz
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