[FFmpeg-devel] Fix ctts_index calculation

[Xiaohan Wang (王消寒)]

I uploaded a new patch. Is this what you meant?

I am confused with the code though. In the case *ctts_index == ctts_count,
this while loop will do nothing. Is this what we want? Also, the "wrong"
|ctts_index| will be available outside of this function. How do we make
sure it won't cause trouble later?

On Fri, Feb 9, 2018 at 12:26 PM, Sasi Inguva <isasi-at-google.com at ffmpeg.org
> wrote:

> >
> > diff --git a/libavformat/mov.c b/libavformat/mov.c
> > index 5adba52e08..f0bd3e3623 100644
> > --- a/libavformat/mov.c
> > +++ b/libavformat/mov.c
> > @@ -3148,7 +3148,7 @@ static int find_prev_closest_index(AVStream *st,
> >          *ctts_index = 0;
> >          *ctts_sample = 0;
> >          for (index_ctts_count = 0; index_ctts_count < *index;
> > index_ctts_count++) {
> > -            if (*ctts_index < ctts_count) {
>
> +            if (*ctts_index < ctts_count - 1) {
> >
> If you do this, then we are skipping, looking at ctts_samples in the last
> ctts entry where (*ctts_index == ctts_count -1), which is not desired.
>
>                  (*ctts_sample)++;
> >                  if (ctts_data[*ctts_index].count == *ctts_sample) {
> >                      (*ctts_index)++;
> >
>
> Here *ctts_index == ctts_count  only iff   the *ctts_index is the last CTTS
> entry, and we still didn't reach   *index. That means that it's file with
> CTTS truncated i.e. no corresponding CTTS entries for some STTS entries.
> This issue can be fixed by checking for  *ctts_index <  ctts_count, in the
> line after this loop.
> while (*index
> <https://cs.corp.google.com/piper///depot/google3/third_
> party/ffmpeg/next/libavformat/mov.c?l=3123&ct=xref_jump_to_
> def&gsn=index&rcl=184932376>
> >= 0 && (*ctts_index
> <https://cs.corp.google.com/piper///depot/google3/third_
> party/ffmpeg/next/libavformat/mov.c?l=3124&ct=xref_jump_to_
> def&gsn=ctts_index&rcl=184932376>)
> >= 0) {
> we already check for (*ctts_index) >=0 so we can check for the upper bound
> too.
>
> On Sat, Feb 3, 2018 at 12:36 PM, Michael Niedermayer
> <michael at niedermayer.cc
> > wrote:
>
> > On Fri, Feb 02, 2018 at 05:55:38PM -0800, Xiaohan Wang (王消寒) wrote:
> > >
> >
> > >  mov.c |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 87157b4053de0e044e78db72ef13e8058075c235
> 0001-Fix-ctts_index-calculatio
> > n.patch
> > > From bb376fd2de5da5f9ecdef41621a579252b899d7d Mon Sep 17 00:00:00 2001
> > > From: Xiaohan Wang <xhwang at chromium.org>
> > > Date: Fri, 2 Feb 2018 17:33:56 -0800
> > > Subject: [PATCH] Fix ctts_index calculation
> > >
> > > An index should never be equal to the count. Hence we must make sure
> > > *ctts_index < ctts_count.
> > > ---
> > >  libavformat/mov.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > should be reviewed by sasi idealy, he wrote this
> >
> > thx
> >
> >
> > [...]
> >
> > --
> > Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> >
> > Democracy is the form of government in which you can choose your dictator
> >
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