[FFmpeg-devel] [PATCH]Auto-detection for concat demuxer

Nicolas George nicolas.george at normalesup.org
Tue Feb 5 20:30:14 CET 2013

Le sextidi 16 pluviôse, an CCXXI, Michael Niedermayer a écrit :
> we could have 2 demuxers
> foobar and foobar-autoprobe
> first would never autoprobe and second would enable safe mode

Yes, that would work, that is an interesting idea.

But is it worth it? It is quite hackish (and possibly brittle: it can hinder
future evolutions of the probing system, or be broken by unrelated changes),
and may prove confusing for the users (why are there two demuxers for the
same format, why do they behave slightly differently?), for a benefit that
appears to me very small.

If I had been less lazy and implemented file signature, filename checking
and probing right from the start, this discussion would not have happened.

Also, I think that the current syntax, without the signature line, is too
ambiguous: a completely unrelated file can easily look like a concat script.
Also, maintaining the guessing-probing function for syntax extensions would
require work, again for a benefit that I fail to see.

Last point, that I failed to notice until now: Carl's proposal only
recognize when the "file" keyword is at the beginning of the line and
followed by a space, while the demuxer accepts leading spaces and/or a tab
afterwards. That is easy to fix, of course, but I believe it illustrates how
this kind of probing is a maintenance burden.

I really think that having a fixed signature line and probing based only on
it is the cleanest way.


  Nicolas George
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