[FFmpeg-devel] [PATCH 2/3] lavd/utils: always look at file extension when probing

[Anton Khirnov]

On Sat, Nov 13, 2010 at 10:39:44AM +0100, Reimar D?ffinger wrote:
> On Sat, Nov 13, 2010 at 10:22:38AM +0100, Anton Khirnov wrote:
> > On Fri, Nov 12, 2010 at 07:15:17PM +0100, Michael Niedermayer wrote:
> > > On Fri, Nov 12, 2010 at 06:18:10PM +0100, Anton Khirnov wrote:
> > > > ---
> > > >  libavformat/utils.c |    5 +++--
> > > >  1 files changed, 3 insertions(+), 2 deletions(-)
> > > 
> > > rejected
> > > this can (and i wager a bet it will) break things.
> > what would it break?
> 
> Values indicating an unsure detection will suddenly become values indicating
> a certain detection.
> In case of e.g. MP3 or DV and only let's say the first 12 bytes of a file
> in the probe buffer that is almost certain to result in false positives.
> 
> > > and you provide no example that it fixes so its same or worse than svn
> > This is related to the issue i mentioned before -- files with huge id3v2
> > headers fail to be detected if the buffer isn't large enough. Yes i know
> > the solution is to provide a bigger buffer, but IMO lavf should do the
> > best possible guess with the information it has and that includes the
> > file extension.
> 
> File extension can never make a detection reliable, which AFAICT your
> patch would pretend to.
> Neither can it resolve a conflict if two formats are detected with
> low probability.
> And it probably shouldn't be considered a conflict if a format
> is only detected with low probability but that does not match
> the extension (consider a wav/RIFF file containing MP3, and a lot of
> people will give that a .mp3 extension on top. I have also seen
> AVI with .mp2, raw MPEG-4 with .mp4, DV in mov with .dv, all
> of which have a high risk that this extension "offset" will
> make the detection break).
> 
> > Anyway, if you're dead set against using file extensions, why are they
> > even there?
> 
> They're useful information, but your implementation gives them almost
> the same priority as the probe function itself, that is not appropriate.
I merely copied the number that was already there.
Would the attached patch be more acceptable then? An extension adds 25%
to the score, up to 50% max.

-- 
Anton Khirnov
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