[FFmpeg-devel] [PATCH 2/3] avcodec/fmvc: buffer size is stride based not 4*width

[Paul B Mahol]

On Fri, Sep 2, 2022 at 6:32 PM Michael Niedermayer <michael at niedermayer.cc>
wrote:

> On Mon, Jun 13, 2022 at 09:13:19PM +0200, Michael Niedermayer wrote:
> > On Mon, Jun 13, 2022 at 12:10:44PM +0200, Paul B Mahol wrote:
> > > On Mon, Jun 13, 2022 at 11:48 AM Anton Khirnov <anton at khirnov.net>
> wrote:
> > >
> > > > Quoting Paul B Mahol (2022-06-13 11:34:44)
> > > > > On Mon, Jun 13, 2022 at 11:10 AM Anton Khirnov <anton at khirnov.net>
> > > > wrote:
> > > > >
> > > > > > Quoting Paul B Mahol (2022-06-13 10:04:04)
> > > > > > > On Sat, Jun 11, 2022 at 4:55 PM Michael Niedermayer <
> > > > > > michael at niedermayer.cc>
> > > > > > > wrote:
> > > > > > >
> > > > > > > > On Sat, Jun 11, 2022 at 10:47:57AM +0200, Paul B Mahol wrote:
> > > > > > > > > Have you actually tested this "change" ?
> > > > > > > >
> > > > > > > > On every file i found
> > > > > > > > 6-methyl-5-hepten-2-one-CC-db_small.avi
> > > > > > > > fmvcVirtualDub_small.avi
> > > > > > > > skrzyzowanie4.avi
> > > > > > > > fmvc-poc.avi
> > > > > > > >
> > > > > > > > are there any other files i should test it on ?
> > > > > > > >
> > > > > > >
> > > > > > > Yes, the ones where stride != width.
> > > > > >
> > > > > > Give examples of such files then. And add more tests.
> > > > > >
> > > > > > You really should try to be more helpful if you care about this
> code
> > > > > > working.
> > > > >
> > > > >
> > > > > Code works perfectly from start. There are always attempts to
> break it.
> > > > > Your attempts to belittle my work are futile.
> > > >
> > > > Perfect code should live in an external repository that is locked
> > > > against modification.
> > > >
> > > > The ffmpeg repository is only for imperfect code that evolves with
> time,
> > > > and so requires changes.
> > > >
> > > >
> > > I dunno what Michael attempts to fix. Decoder works fine with valid
> files.
> > > I doubt that encoder would encode random bytes or padding into valid
> file
> > > bitstream.
> >
> > the stride*4 / width*4 change was because of 2 things.
> > first with AV_PIX_FMT_BGR24 the data stored is not width*4
> >
> > stride is in units of 4 bytes for some reason, so stride*4
> > fixes this
> > The 2nd issue is that the code addresses it by "s->stride * 4"
> > so the buffer allocation should be stride*4 if we belive the
> > other code is correct
> >
> >         src = s->buffer;
> > ...
> >         for (y = 0; y < avctx->height; y++) {
> > ...
> >             src += s->stride * 4;
> >
> > width*4 works because its bigger than stride*4 for BGR24 which is what
> all
> > samples i have use.
> >
> > also
> >         ssrc = s->buffer;
> >         ...
> >         for (y = 0; y < avctx->height; y++) {
> >             ...
> >             ssrc += s->stride * 4;
> > and
> >         dst = (uint32_t *)s->buffer;
> >
> >         for (block = 0, y = 0; y < s->yb; y++) {
> >             int block_h = s->blocks[block].h;
> >             uint32_t *rect = dst;
> >
> >             for (x = 0; x < s->xb; x++) {
> >                 int block_w = s->blocks[block].w;
> >                 uint32_t *row = dst;
> >
> >                 block_h = s->blocks[block].h;
> >                 if (s->blocks[block].xor) {
> >                     for (k = 0; k < block_h; k++) {
> >                         uint32_t *column = dst;
> >                         for (l = 0; l < block_w; l++)
> >                             *dst++ ^= *src++;
> >                         dst = &column[s->stride];
> >                     }
> >                 }
> >                 dst = &row[block_w];
> >                 ++block;
> >             }
> >             dst = &rect[block_h * s->stride];
> >         }
> >
> > Again, if you have fmvc files with more odd widths or other pixel formats
> > these would be very welcome. I can just say the code as is in git is
> wrong
> > and the buffer size as is in git is wrong. I noticed this when i added
> > a check to see if the buffer is only partly filled and realized its
> > always partly filled even when the whole image is actually touched
>
> If there are no objections aka noone sees a bug in this then id like
> to apply this
>

Since when are partially filled buffers are bad thing?

>
> thx
>
> [...]
>
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> What does censorship reveal? It reveals fear. -- Julian Assange
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