[FFmpeg-devel] [PATCH] lavfi: add avfilter_copy_frame_props()

[Stefano Sabatini]

On date Thursday 2011-05-05 01:27:19 +0200, Michael Niedermayer encoded:
> On Thu, May 05, 2011 at 01:08:55AM +0200, Stefano Sabatini wrote:
> > On date Tuesday 2011-05-03 01:49:19 +0200, Michael Niedermayer encoded:
> > > On Tue, May 03, 2011 at 12:20:48AM +0200, Stefano Sabatini wrote:
> > > > On date Tuesday 2011-05-03 00:06:11 +0200, Michael Niedermayer encoded:
> > > > > On Mon, May 02, 2011 at 07:26:13PM +0200, Stefano Sabatini wrote:
> > > > > > On date Monday 2011-05-02 12:42:04 +0200, Michael Niedermayer encoded:
> > > > > > > On Sun, May 01, 2011 at 04:29:54PM +0200, Stefano Sabatini wrote:
> > > > > > [...] 
> > > > > > > >  ffmpeg.c                  |    1 
> > > > > > > >  ffplay.c                  |    5 ++--
> > > > > > > >  libavfilter/Makefile      |    2 -
> > > > > > > >  libavfilter/avcodec.h     |   50 ++++++++++++++++++++++++++++++++++++++++++++++
> > > > > > > 
> > > > > > > isnt it possible to just always install libavcodec/avcodec.h even
> > > > > > > if libavcodec is disabled?
> > > > > > 
> > > > > > I would prefer to avoid hacking configure and keep the dependency on
> > > > > > libavcodec strict, AVFrame should be used only if libavcodec is used,
> > > > > > so I'd prefer not to make distinctions between compile-time and
> > > > > > running-time dependencies (and we could need at some point the use of
> > > > > > some function from libavcodec).
> > > > > 
> > > > 
> > > > > is this change needed at all? #include "libavcodec/avcodec.h" in
> > > > > libavfilter should use the non installed header and no installed
> > > > > header from libavfilter shouldneed  libavcodec/avcodec.h for a struct
> > > > > pointer
> > > > > am i missing something ?
> > > > 
> > > > Do you mean something like this:
> > > > 
> > > > struct AVFrame;
> > > > 
> > > > static inline
> > > > void avfilter_copy_frame_props(AVFilterBufferRef *dst, const AVFrame *src);
> > > 
> > > i was thinking of
> > > void avfilter_copy_frame_props(AVFilterBufferRef *dst, const struct AVFrame *src);
> > 
> > Sorry I can't see the point of avoiding #include
> > "libavcodec/avcodec.h" when the file is supposed to be used only when
> > avcodec.h is used in the application, in other words you can avoid
> > including libavcodec/avcodec.h, but the application will *have* to do
> > it anyway, and even if you don't include it I can't see the advantage.
> 
> the advantage is that we dont have a interdependancy in the headers
> a user application can use libavfilter on a system without libavcodec
> just not easily avfilter_copy_frame_props()
> If the system has both installed a user app can use all.
> 
> including the libavcodec header from libavfilter/avcodec.h will
> require libavcodec/avcodec.h to be installed when libavfilter is
> installed so you either have libavfilter depend on libavcodec or
> have to install libavcodec/avcodec.h even when libavcodec is not.
> 
> but maybe i miss an option.

It the user wants to use libavfilter without libavcodec, she
configures FFmpeg with --disable-libavcodec and compiles, libavfilter
is compiled but the libavfilter/avcodec.o module is not compiled in
(and thus avfilter_copy_frame_props won't be available at run-time).

In the application she won't need AVFrame, *and* she won't include
libavfilter/avcodec.h, so no need to have libavcodec/avcodec.h
installed.

If she wants libavfilter+libavcodec, she will configure/compile FFmpeg
with --enable-avcodec, and will include libavcodec/avcodec.h. Since
she's already using libavcodec in her application, avoiding
libavcodec/avcodec.h inclusion in libavfilter/avcodec.h is pointless.

In case she may need libavfilter/libavcodec conditionally, she can
implement the inclusion logic in the application:
#if CONFIG_AVCODEC
#include "libavfilter/avcodec.h"
#endif

and do the same in the code.

Of course in order to avoid missing symbols problems, libavfilter
compiled for a distro should always enable libavcodec, but this is
definitively not required for custom projects.
-- 
FFmpeg = Frightening & Fierce Mean Power Experimenting Generator
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