[MPlayer-dev-eng] PATCH: XviD/OpenDivX vs mplayer namespace clash

[Chris Bednar]

On Sun, 6 Jan 2002, Arpi wrote:

> but i don't really understand the sense of this patch.
> opendivx decode is NOT compiled and linked if external divx4/odivx/xvid liek
> library is used. and even if it would be linked, it won't eb used as both
> libs use encore() and decore() functions so they always clash...

    The problem is not a clash between the two libraries, but a 
namespace problem with mplayer. The opendivx lib defines global
variables named `idct' and `postprocess', and mplayer has functions
with these names. This causes a classic GNU linker problem; when
you try to write to the variable, you get a sig11. Try this:

/*File read.c: gcc -o read read.c*/

  extern int read;
  int main (int argc, char **argv)
  {
    read = 1;
    return (0);
  }

It will compile and link, even tho you haven't defined the variable.
It will gleefully segfault in your face, too, because you just tried
to write into code-space, namely, the read() call.

   Companies use this kind of little snip to sell their commercial
compilers.

   Although it's a pain in the ass, a general-purpose library shouldn't
define globals at all, but it definitely shouldn't define globals without
hideous prefixes...



> so i see no sense of patching decore/* to get xvid working, as you cannot
> use both library in hte same mplayer binary.
> currently, if divx4linux is detected/selected then opendivx won't be
> compiled. we should just replace divx4linxu by xvid when it gets stable.
> (last time we tried it just did sig11)

...and so did I, and the above was the reason. Now, if I could
only get the brightness/contrast stuff hacked in, I'd have everything
I need to make me happy (for the next few hours, anyway).



    BTW, I think it would be nice if you guys would liberalize your
CC policy a bit. I interfere with a lot of projects, and if the message
comes in the middle of a mailing-list, I tend to miss it.

    Only if you actually want to hear back from me, of course ;)


---- ``Windows: It does that sometimes.''  -mattdm
Chris J. Bednar
Director, Distributed Computing Product Group
http://AdvancedDataSolutions.com/