[FFmpeg-devel] [Read EXIF metadata 3/3] Read EXIF metadata in JPEG input.

[Michael Niedermayer]

On Sat, Aug 10, 2013 at 01:25:23PM +0200, Thilo Borgmann wrote:
> 
> >> @@ -215,6 +218,8 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
> >>      int len, nb_components, i, width, height, pix_fmt_id;
> >>      int h_count[MAX_COMPONENTS];
> >>      int v_count[MAX_COMPONENTS];
> >> +    AVDictionary **metadata = avpriv_frame_get_metadatap(s->picture_ptr);
> >> +    AVDictionary *tmp;
> >>
> >>      s->cur_scan = 0;
> >>      s->upscale_h = s->upscale_v = 0;
> >> @@ -459,6 +464,10 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
> >>              s->avctx->pix_fmt = AV_PIX_FMT_GRAY16;
> >>      }
> >>
> >> +    // keep metadata alive by hiding AVDictioniary behind *tmp
> >> +    tmp       = *metadata;
> >> +    *metadata = NULL;
> >> +
> >>      av_frame_unref(s->picture_ptr);
> >>      if (ff_get_buffer(s->avctx, s->picture_ptr, AV_GET_BUFFER_FLAG_REF) < 0)
> >>          return -1;
> >> @@ -466,6 +475,9 @@ int ff_mjpeg_decode_sof(MJpegDecodeContext *s)
> >>      s->picture_ptr->key_frame = 1;
> >>      s->got_picture            = 1;
> >>
> >> +    // restore metadata in current buffer
> >> +    *avpriv_frame_get_metadatap(s->picture_ptr) = tmp;
> >> +
> >>      for (i = 0; i < 3; i++)
> >>          s->linesize[i] = s->picture_ptr->linesize[i] << s->interlaced;
> >>
> >
> > this looks quite odd, metadata should only be stored in the correct
> > frame, not the old frame
> 
> Yes a hack. However, my alternative solution does somehow loose
> the metadata after _decode_frame() is finished and I don't know why.......
> attached as follow-up patch 4/3 of rev 5 (0004-Remove-hack).
> So I need another idea or a hint how to fix that alternative.

try to put the copying in case EOI


> 
> 
> >> +        // read all IFDs and store the metadata
> >> +        ifds_read = 0;
> >> +        while ((ifd_offset = ff_exif_decode_ifd(s->avctx, &gbytes, le,
> avpriv_frame_get_metadatap(s->picture_ptr))) > 0) {
> >> +            if (++ifds_read > FF_ARRAY_ELEMS(ifd_tags)) {
> >> +                av_log(s->avctx, AV_LOG_INFO, "mjpeg: found more IFD's in
> EXIF data than expected. Skipping.\n");
> >> +                break;
> >> +            }
> >> +            bytestream2_seek(&gbytes, ifd_offset, SEEK_SET);
> >> +        }
> >
> > I would assume that offsets always move forward but that theres no
> > real limit om the number of tags
> 
> TIFF 6 spec says:
> "This file offset may point anywhere in the file, even after the image data."
> So it might also point backwards again. Also, according to EXIF specs, there are
> exactly these three IFD's defined.

i think there is no requirement that they are just
FF_ARRAY_ELEMS(ifd_tags) ifds in there, also this code potentially
parses entries multiple times before detecting a problem.


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

DNS cache poisoning attacks, popular search engine, Google internet authority
dont be evil, please
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