meson configure option to change dependency path

[gerion0]

I have a project build with meson, that uses parts of FFmpeg, shared libraries installed in the system:

ffmpeg = [
  dependency('libavformat'),
  dependency('libavcodec'),
  dependency('libavutil'),
]
foobar = executable('foobar', 'main.c', dependencies: ffmpeg)

This works. However, I recently discovered a problem in the problem so debugging (and changing) FFmpeg would be useful.

Is there a way to say meson not to link against the system library but link against a self build local version (ideally without changing the meson.build file)?

If not, I would leave this here as a feature request.

I imagine something like:

meson configure --dependency libavformat:"~/src/ffmpeg/":"~/src/ffmpeg/libavformat/libavformat.so"

with the format:

name:include_dirs:link_objects

Additionally, I tried to change the meson.build file to say meson to use "~/src/ffmpeg/libavformat/libavformat.so", but have no success.

ffmpeg_src = '/home/gerion0/src/ffmpeg/'

ffmpeg_inc = include_directories(ffmpeg_src)
libavformat = shared_library(ffmpeg_src + 'libavformat/libavformat.so')
libavutil = shared_library(ffmpeg_src + 'libavutil/libavutil.so')
libavcodec = shared_library(ffmpeg_src + 'libavcodec/libavcodec.so')
ffmpeg_self = declare_dependency(link_with : [libavformat, libavutil, libavcodec],
  include_directories : ffmpeg_inc)

However, changing the meson.build file is (in my opinion) the wrong way, since the meson.build file should specify the normal case and not custom user wanted stuff.

[tp-m]

You would install ffmpeg into a prefix, e.g. in your home directory, and then do export PKG_CONFIG_PATH=/home/you/yourprefix/lib/pkgconfig before running meson. (Might also need an export LD_LIBRARY_PATH=/home/you/yourprefix/lib later when running things to make the dynamic linker find the right libs at runtime)

[gerion0]

Hmm. It seems, that meson compiles with the system libraries:

$ PKG_CONFIG_PATH=/home/gerion0/src/ffmpeg/install/usr/local/lib/pkgconfig/ meson build
...
Dependency libavformat found: YES 58.28.101
Dependency libavcodec found: YES 58.53.101
Dependency libavutil found: YES 56.30.100
$ cd build
$ ninja -v
...
[8/8] ccache cc  -o foobar ... -Wl,--no-undefined -Wl,--as-needed -Wl,--start-group ... /usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../lib64/libavformat.so /usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../lib64/libavcodec.so /usr/lib/gcc/x86_64-pc-linux-gnu/8.2.0/../../../../lib64/libavutil.so -Wl,--end-group

However, with LD_LIBRARY_PATH the linker find the correct libs but I guess, this is only valid as long as the ABI is equal:

$ ldd foobar
  libavformat.so.58 => /home/gerion0/src/ffmpeg/install/usr/local/lib/libavformat.so.58 (0x00007f81be998000)
  libavcodec.so.58 => /home/gerion0/src/ffmpeg/install/usr/local/lib/libavcodec.so.58 (0x00007f81bd676000)
  libavutil.so.56 => /home/gerion0/src/ffmpeg/install/usr/local/lib/libavutil.so.56 (0x00007f81bd57b000)

[tp-m]

You can check what

$ PKG_CONFIG_PATH=/home/.../pkgconfig pkg-config --modversion libavcodec
$ PKG_CONFIG_PATH=/home/.../pkgconfig pkg-config --cflags libavcodec
$ PKG_CONFIG_PATH=/home/.../pkgconfig pkg-config --libs libavcodec

returns. --libs should have -L/prefix/lib bits in it before the -lavcodec* bits.

[gerion0]

Thanks for the hint. That solved my problem. I installed ffmpeg locally with DESTDIR="..." make install. However, the pkg-config files were not respecting this but pointing to /usr/local/lib where ffmpeg was not present. Installing with ./configure --prefix=... fixed this.