[FFmpeg-devel] [PATCH] avformat/img2dec: return immediately in jpeg_probe() when EOI is found

[Matthieu Bouron]

On Wed, Apr 01, 2020 at 07:30:55PM +0200, Carl Eugen Hoyos wrote:
> Am Mi., 1. Apr. 2020 um 19:15 Uhr schrieb Matthieu Bouron
> <matthieu.bouron at gmail.com>:
> >
> > On Wed, Apr 01, 2020 at 06:55:42PM +0200, Carl Eugen Hoyos wrote:
> > > Am Mi., 1. Apr. 2020 um 18:35 Uhr schrieb Matthieu Bouron
> > > <matthieu.bouron at gmail.com>:
> > > >
> > > > On Wed, Apr 01, 2020 at 06:29:03PM +0200, Carl Eugen Hoyos wrote:
> > > > > Am Mi., 1. Apr. 2020 um 18:01 Uhr schrieb Matthieu Bouron
> > > > > <matthieu.bouron at gmail.com>:
> > > > > >
> > > > > > Fixes probing of JPEG files containing MPF metadata appended at the end
> > > > > > of the file.
> > > > > >
> > > > > > The MPF metadata chunk can contains multiple JPEG images (thumbnails)
> > > > > > which makes the jpeg_probe fails (return 0) because it finds a SOI
> > > > > > marker after EOI.
> > > > > > ---
> > > > > >
> > > > > > This patch fixes probing of JPEG files containing MPF metadata [1] appended
> > > > > > at the end of the file.
> > > > > >
> > > > > > Such files can be produced by GoPro camera (which produces JPEG files
> > > > > > with MPF metadata).
> > > > > >
> > > > > > You can find a sample here:
> > > > > > https://0x5c.me/gopro_jpg_mpf_probe_fail
> > > > >
> > > > > The sample works fine here with FFmpeg 4.2: Is there a regression?
> > > >
> > > > This sample does not work on FFmpeg 4.2 and master if you set a big
> > > > enought formatprobesize (which matches the file size of the sample):
> > >
> > > Inlined is a patch that fixes detection but I wonder if this shouldn't be
> > > detected as mjpeg instead
> > >
> > > Carl Eugen
> > >
> > > diff --git a/libavformat/img2dec.c b/libavformat/img2dec.c
> > > index 40f3e3d499..4e63b3494e 100644
> > > --- a/libavformat/img2dec.c
> > > +++ b/libavformat/img2dec.c
> > > @@ -737,20 +737,22 @@ static int j2k_probe(const AVProbeData *p)
> > >  static int jpeg_probe(const AVProbeData *p)
> > >  {
> > >      const uint8_t *b = p->buf;
> > > -    int i, state = SOI;
> > > +    int i, state = SOI, MPF = 0;
> > >
> > >      if (AV_RB16(b) != 0xFFD8 ||
> > >          AV_RB32(b) == 0xFFD8FFF7)
> > >      return 0;
> > >
> > >      b += 2;
> > > -    for (i = 0; i < p->buf_size - 3; i++) {
> > > +    for (i = 0; i < p->buf_size - 8; i++) {
> > >          int c;
> > >          if (b[i] != 0xFF)
> > >              continue;
> > >          c = b[i + 1];
> > >          switch (c) {
> > >          case SOI:
> > > +            if (state == EOI && MPF)
> > > +                return AVPROBE_SCORE_EXTENSION + 1;
> >
> > Your patch might work
> 
> You could test it.
> 
> > but the code is trying to find JPEG markers in the
> > MPF metadata until we reach the first EOI in the MPF JPEG thumbnails,
> 

I meant SOI sorry.

> No, and I am quite sure that I tested this sufficiently.

My point is, we are trying to parse way more data than necessary (the data
we parse might not be jpeg at this point): the code looks for a marker and
handles it, if the marker is unknown it repeats this operation for the
next byte until it reaches the end of the buffer or it finds SOI in the
EOI+MPF state (with your patch).

Why cant' we end the processing at EOI ? If there is a particular reason
for that ?

> 
> Shouldn't there be a mpf demuxer that also provides the attachments?

I already have a patch to parse the MPF metadata. The only thing left to
do is to expose the attachments (it currently only exposes those as
file offsets in stream metadata). I will send the patch later on.

> 
> Carl Eugen
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-- 
Matthieu B.