[Libav-user] Can not link ffmpeg without pkg-config

[Perette Barella]

> Then I can compile and link using the following command line:
> gcc  -o ffmpeg_grabber ffmpeg_grabber_03.c -Wall -ggdb $(pkg-config --cflags libavformat libavcodec libswresample libswscale libavutil sdl) $(pkg-config --libs libavformat libavcodec libswresample libswscale libavutil sdl) -lm 
> 
> But I have a lot of link errors (undefined a lot of things) removing pkg-config:
> gcc  -o test test.c -Wall -lavformat -lavcodec -lswresample -lswscale -lavutil -lm
> 
> The question is: How to avoid undefine errors without using the pkg-config?

When static linking, you need to link not only the ffmpeg libraries themselves, but all the libraries that they link to in turn.  In this command:
> pkg-config --libs libavformat libavcodec libswresample libswscale libavutil sdl


`pkg-config --libs` gets the link flags necessary (there’s also a --cflags option too), including all those indirectly needed libraries, to link.  You can run pkg-config --libs on the command line to see the list.

This list will not always be the same.  My Mac, for example, includes pthreads among the automatically-linked system libraries, so there will be no ‘-lpthreads’, but it includes -L/opt/local/lib, because it’s installed in a non-default place where the linker won’t look.  Link flags also depend on what ffmpeg was configured and built with: for example, if libfoobar is installed, there could be a dependency for -lfoobar; but if missing when I ran ./configure on ffmpeg, then I might have ffmpeg but without whatever capabilities foobar provides.  `configure` scripts see what’s available and build what they can, and they often utilize information from pkg-config where it’s available.

I wonder *why* are you avoiding pkg-config? Are you planning to build/compile on a system without it?  Are you thinking of a portable `configure` script, and considering what to do if pkg-config is missing?  Because pkg-config came about to solve the problem you’re running into.  I’ve seen some debate about whether pkg-config solves the problem right, but it is the thing in place and trying to avoid it is to make yourself problems.  Not using it means a lot of extra trouble, so unless you have a *really* good reason...

Perette