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

[Michael Niedermayer <michael@niedermayer.cc>]

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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@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@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@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

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

What does censorship reveal? It reveals fear. -- Julian Assange

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