[FFmpeg-devel] [Bulk] [PATCH] avformat/mxfdec: dont truncate packets

[Michael Niedermayer]

On Mon, Feb 03, 2014 at 11:15:43AM +0100, Tomas Härdin wrote:
> On Thu, 2014-01-30 at 21:08 +0100, Michael Niedermayer wrote:
> > On Thu, Jan 30, 2014 at 07:45:19PM +0100, Tomas Härdin wrote:
> > > On Thu, 2014-01-30 at 02:39 +0100, Michael Niedermayer wrote:
> > > > On Wed, Jan 29, 2014 at 10:20:48AM +0100, Tomas Härdin wrote:
> > > > > On Tue, 2013-11-05 at 07:57 +0000, Tim Nicholson wrote:
> > > > > > On 24/10/13 20:28, Michael Niedermayer wrote:
> > > > > > > Fixes Ticket2776
> > > > > > > 
> > > > > > > Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> > > > > > > ---
> > > > > > >  libavformat/mxfdec.c |    1 -
> > > > > > >  1 file changed, 1 deletion(-)
> > > > > > > 
> > > > > > > diff --git a/libavformat/mxfdec.c b/libavformat/mxfdec.c
> > > > > > > index d0cbeea..59e5c0d 100644
> > > > > > > --- a/libavformat/mxfdec.c
> > > > > > > +++ b/libavformat/mxfdec.c
> > > > > > > @@ -2285,7 +2285,6 @@ static int mxf_read_packet_old(AVFormatContext *s, AVPacket *pkt)
> > > > > > >                                        "KLV for edit unit %i extending into "
> > > > > > >                                        "next edit unit",
> > > > > > >                                        mxf->current_edit_unit);
> > > > > > > -                klv.length = next_ofs - avio_tell(s->pb);
> > > > > > >              }
> > > > > > >  
> > > > > > >              /* check for 8 channels AES3 element */
> > > > > > > 
> > > > > > 
> > > > > > Sorry for a very late review, but I have been snowed under (with a
> > > > > > project using ffv1 v3 you may be pleased to hear) and after a quick
> > > > > > glance it didn't feel right and I wanted to delve further.
> > > > > > 
> > > > > > We go to the bother of performing a test to trap (an admittdedly
> > > > > > unusual) case, and then if it happens do not introduce the safety net to
> > > > > > avoid an error. It would be better to work out why a false positive is
> > > > > > occuring with the sample and fix that, otherwise we will reintroduce the
> > > > > > issue this segment of code was trying to fix.
> > > > > > 
> > > > > > Does Tomas have a view? the original code to trap the misreading of OP
> > > > > > Atom was his.
> > > > > 
> > > > > Sorry for the extremely late reply. But yes, that piece of code is there
> > > > > to deal with certain bad files. I don't remember if we/I have samples
> > > > > for it, but I trust my old self put it there for good reasons.
> > > > > 
> > > > > As for a proper fix, my MXF is a bit rusty. But I think this ties into a
> > > > > thing I had in mind a while back, which was to introduce a huge table
> > > > > mapping all EssenceContainer ULs to the corresponding wrapping kind
> > > > > (relying on byte 15 of the UL is incorrect). I don't think relying on
> > > > > OperationalPattern is enough to determine if the file is clip wrapped or
> > > > > frame wrapped, and the MXF specs are vague on this matter (as usual).
> > > > > Mistaking clip wrapped essence for being frame wrapped is what that
> > > > > piece of code is about.
> > > > > 
> > > > 
> > > > > I think I put some random unfinished code on this mailing list for
> > > > > generating the EssenceContainer -> WrappingKind tables described above.
> > > > > The problem then is that they will grow the binary by about half a
> > > > > megabyte..
> > > > 
> > > > if the tables can be generated and the generation code is smaller
> > > > than the tables then the space problem should be avoidable
> > > 
> > > IIRC the tables are generated from Excel files via a perl script, so
> > > that's runtime generation is not going to work
> > 
> > adding 500kb for this doesnt sound very nice :(
> > 
> > is there no other way to find the wraping kind,
> > without reling on the ULs ?
> > or am i missing something here
> 
> Sometimes you can just inspect byte 15 of the UL, but not always.
> Perhaps some sort of hybrid solution? Like check a table with special
> cases first, then byte 15 if no match was found. Then we can add entries
> to that table when we run across samples for them. Or maybe the Excel
> file can be put through some clever program that figures out the special
> cases. The UL's are highly hierarchical, so some kind of decision tree
> could also work

Can you post the 2 lists here or provide a link to them ?
maybe someone can figure out how to seperate them with a minimum of
code. Might even make a good gsoc qualification task

Also can this not be done without using the UL ?

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Concerning the gods, I have no means of knowing whether they exist or not
or of what sort they may be, because of the obscurity of the subject, and
the brevity of human life -- Protagoras
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