[FFmpeg-devel] [RFC PATCH v4 2/5] libavcodec/j2kenc: Fix tag tree coding

[Gautam Ramakrishnan]

On Tue, Aug 25, 2020 at 1:18 PM Michael Niedermayer
<michael at niedermayer.cc> wrote:
>
> On Tue, Aug 25, 2020 at 09:50:04AM +0530, gautamramk at gmail.com wrote:
> > From: Gautam Ramakrishnan <gautamramk at gmail.com>
> >
> > The implementation of tag tree encoding was incorrect.
> > However, this error was not visible as the current j2k
> > encoder encodes only 1 layer.
> > This patch fixes tag tree coding for JPEG2000 such tag
> > tree coding would work for multi layer encoding.
> > ---
> >  libavcodec/j2kenc.c   | 41 +++++++++++++++++++++++++----------------
> >  libavcodec/jpeg2000.c |  1 +
> >  libavcodec/jpeg2000.h |  1 +
> >  3 files changed, 27 insertions(+), 16 deletions(-)
>
> iam not sure the tag tree is working correctly before or after this
>
> For example if i make this chnage:
>
> --- a/libavcodec/j2kenc.c
> +++ b/libavcodec/j2kenc.c
> @@ -282,6 +282,7 @@ static void tag_tree_update(Jpeg2000TgtNode *node)
>      while (node->parent){
>          if (node->parent->val <= node->val)
>              break;
> +        abort();
>          node->parent->val = node->val;
>          node = node->parent;
>          lev++;
>
> all tests still pass, so iam not sure what sets the parent values or if
> they are not if the code working with them is fully tested
Looks like the tag tree initializer is incorrect. This would not cause an
undecodable file, but however, leads to an extremely inefficient encoding
of the tag tree. I shall send a patch for this also.
>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
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-- 
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Gautam |