[FFmpeg-devel] [PATCH] lavc/aac: fix shared build failures with MSVC.

[Hendrik Leppkes]

On Fri, Nov 9, 2012 at 4:44 AM, Ronald S. Bultje <rsbultje at gmail.com> wrote:

> Hi,
>
> On Thu, Nov 8, 2012 at 7:42 PM, Ronald S. Bultje <rsbultje at gmail.com>
> wrote:
>
> > On Thu, Nov 8, 2012 at 4:18 PM, Michael Niedermayer <michaelni at gmx.at
> >wrote:
> >
> >> On Fri, Nov 09, 2012 at 12:09:56AM +0100, Clément Bœsch wrote:
> >> > ---
> >> >  libavcodec/aacenc.c       | 9 ++++++++-
> >> >  libavcodec/libvo-aacenc.c | 9 ++++++++-
> >> >  2 files changed, 16 insertions(+), 2 deletions(-)
> >> >
> >> > diff --git a/libavcodec/aacenc.c b/libavcodec/aacenc.c
> >> > index fe5b84d..22962a3 100644
> >> > --- a/libavcodec/aacenc.c
> >> > +++ b/libavcodec/aacenc.c
> >> > @@ -811,6 +811,13 @@ static const AVClass aacenc_class = {
> >> >      LIBAVUTIL_VERSION_INT,
> >> >  };
> >> >
> >> > +/* duplicated from avpriv_mpeg4audio_sample_rates to avoid shared
> build
> >> > + * failures */
> >>
> >> please also add such a comment to avpriv_mpeg4audio_sample_rates
> >> or maybe move the 2 lines of sample rates in a header and inlcude that.
> >>
> >> I naively assume that theres no clean solution without duplication
> >>
> >
> > That assumption is wrong.
> >
>
> More specifically,
> http://fate.libav.org/i686-msvc-10-dll-wine/20121108195907 works fine?
>
> Ronald
>

But thats libav, and it doesn't have the sample rates in the AVCodec
definition.

The problem is that the dllimport marker is always present, so even if you
use a datasymbol in the same library where it lives, the compiler/linker
make it an imported symbol, which means its not constant, and thus cannot
be used as a static initializer.

A "clean" solution would be to define av_export conditionally, but that
solution was apparently not liked, and instead the permanent define won.

- Hendrik