[FFmpeg-devel] [PATCH] png parser

[Michael Niedermayer]

On Thu, Jun 25, 2009 at 12:59:07PM +0200, Peter Holik wrote:
> Michael Niedermayer schrieb:
> > On Wed, Jun 24, 2009 at 05:54:17PM +0200, Peter Holik wrote:
> >> Michael Niedermayer schrieb:
> > [...]
> >> >> +            if (*state64_ptr == PNGSIG || *state64_ptr == MNGSIG) {
> >> >> +                i++;
> >> >> +                if (ppc->pc.index) {
> >> >> +                    i -= 8;
> >> >> +                    next = i;
> >> >> +                } else {
> >> >> +                    ppc->pc.frame_start_found = 1;
> >> >> +                    ppc->chunk_index = 1;
> >> >> +                    if (i == 8)
> >> >> +                        break;
> >> >> +                    else if (i > 8) {
> >> >> +                        buf += i - 8;
> >> >> +                        buf_size = 8;
> >> >> +                    } else /* if (i < 8) */
> >> >> +                        buf_size = i;
> >> >> +                }
> >> >> +                ff_combine_frame(&ppc->pc, next, &buf, &buf_size);
> >> >> +                return i;
> >> >
> >> > could you explain why this is not just looking like lets say mpeg4:
> >> >
> >> >     if(!vop_found){
> >> >         for(i=0; i<buf_size; i++){
> >> >             state= (state<<8) | buf[i];
> >> >             if(state == 0x1B6){
> >> >                 i++;
> >> >                 vop_found=1;
> >> >                 break;
> >> >             }
> >> >         }
> >> >     }
> >>
> >> png signature is 8 Bytes
> >
> > s/state/state64/ in the example, the question stays the same
> >
> >
> >>
> >>
> >> > what is the point of all the special cases?
> >>
> >>
> >> Because this png parser should filter out good png images.
> >
> > thats not the job of a parser, besides good is a fuzzy term, a
> > png with a bit fliped in the signature is pretty good and easy to decode
> > your code would drop it i think.
> 
> Following parser also drops:
> 
> mpegaudio_parser.c
> mlp_parser.c
> dvbsub_parser.c
> pnm_parser.c
> 
> why may my parser not drop?

i have explained it already
because it drops things that can still be decoded easily in principle
the others you quote may very well be buggy


> 
> Anyway fighting against windmills is meaningless.
> 
> Here now a version without dropping anything and using 32 Bits for
> signature check instead of 64 Bits.

why 32bit?
isnt 64bit simpler for 64bit sigs?

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you think the mosad wants you dead since a long time then you are either
wrong or dead since a long time.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: Digital signature
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20090625/4da44442/attachment.pgp>