Fix build using system ffmpeg when ffmpeg include dirs are empty and fix undefined reference to boost::log

[nerijus]

No description provided.

[nerijus]

Found 2 issues on CentOS 9. First one - I get link error with static boost:

[100%] Linking CXX executable casparcg
/usr/bin/ld: /usr/lib64/libboost_log_setup.a(init_from_settings.o): in function `boost::log::v2s_mt_posix::(anonymous namespace)::default_syslog_sink_factory<char>::create_sink(boost::log::v2s_mt_posix::basic_settings_section<char> const&)':
(.text[.text.group]+0x2cb9): undefined reference to `boost::log::v2s_mt_posix::sinks::syslog_backend::set_severity_mapper(boost::log::v2s_mt_posix::aux::light_function<boost::log::v2s_mt_posix::sinks::syslog::level (boost::log::v2s_mt_posix::record_view const&)> const&)'
/usr/bin/ld: (.text[.text.group]+0x30ae): undefined reference to `boost::log::v2s_mt_posix::sinks::syslog_backend::set_target_address(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned short)'
/usr/bin/ld: (.text[.text.group]+0x314e): undefined reference to `boost::log::v2s_mt_posix::sinks::syslog_backend::set_local_address(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned short)'
/usr/bin/ld: /usr/lib64/libboost_log_setup.a(init_from_settings.o): in function `boost::log::v2s_mt_posix::(anonymous namespace)::default_syslog_sink_factory<wchar_t>::create_sink(boost::log::v2s_mt_posix::basic_settings_section<wchar_t> const&)':
(.text[.text.group]+0x36a9): undefined reference to `boost::log::v2s_mt_posix::sinks::syslog_backend::set_severity_mapper(boost::log::v2s_mt_posix::aux::light_function<boost::log::v2s_mt_posix::sinks::syslog::level (boost::log::v2s_mt_posix::record_view const&)> const&)'
/usr/bin/ld: (.text[.text.group]+0x3ae8): undefined reference to `boost::log::v2s_mt_posix::sinks::syslog_backend::set_target_address(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned short)'
/usr/bin/ld: (.text[.text.group]+0x3bd0): undefined reference to `boost::log::v2s_mt_posix::sinks::syslog_backend::set_local_address(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned short)'
...

The issue is in FindBoost module in cmake. See boostorg/log#46 (comment) and https://gitlab.kitware.com/cmake/cmake/-/issues/20638.
Without this patch link command looks like this:

/usr/bin/c++ -O3 -DNDEBUG CMakeFiles/casparcg.dir/main.cpp.o CMakeFiles/casparcg.dir/server.cpp.o CMakeFiles/casparcg.dir/linux_specific.cpp.o -o casparcg   -L/opt/ffmpeg/lib  ... /usr/lib64/libboost_log.a /usr/lib64/libboost_locale.a /usr/lib64/libboost_regex.a /usr/lib64/libboost_date_time.a /usr/lib64/libboost_coroutine.a /usr/lib64/libboost_atomic.a /usr/lib64/libboost_log_setup.a ...

As you can see /usr/lib64/libboost_log_setup.a is included after /usr/lib64/libboost_log.a. With this PR the order is reversed and linking works correctly.

[nerijus]

2nd issue is that pkgconf libavcodec --cflags does not output anything, probably because it should output -I/usr/include, but because /usr/include is included by default in current distros it is skipped. My /usr/lib64/pkgconfig/libavcodec.pc looks like this:

prefix=/usr
exec_prefix=${prefix}
libdir=/usr/lib64
includedir=/usr/include

Name: libavcodec
Description: FFmpeg codec library
Version: 59.37.100
...
Libs: -L${libdir}  -lavcodec
Libs.private: -lvpx -lm...
Cflags: -I${includedir}

$ pkgconf libavcodec --libs
-lavcodec 
$ pkgconf libavcodec --cflags
<empty line>

I modified FindFFmpeg.cmake like this:

diff --git a/src/CMakeModules/FindFFmpeg.cmake b/src/CMakeModules/FindFFmpeg.cmake
index a5560d808..a09cf6cdb 100644
--- a/src/CMakeModules/FindFFmpeg.cmake
+++ b/src/CMakeModules/FindFFmpeg.cmake
@@ -42,11 +42,13 @@ endif ()
 # Marks the given component as found if both *_LIBRARIES AND *_INCLUDE_DIRS is present.
 #
 macro(set_component_found _component )
+  message(STATUS "${_component}_LIBRARIES=${${_component}_LIBRARIES}")
+  message(STATUS "${_component}_INCLUDE_DIRS=${${_component}_INCLUDE_DIRS}")
   if (${_component}_LIBRARIES AND ${_component}_INCLUDE_DIRS)
-    # message(STATUS "  - ${_component} found.")
+    message(STATUS "  - ${_component} found.")
     set(${_component}_FOUND TRUE)
   else ()
-    # message(STATUS "  - ${_component} not found.")
+    message(STATUS "  - ${_component} not found.")
   endif ()
 endmacro()

and got such output:

$ cmake -DUSE_SYSTEM_FFMPEG=ON ../src
-- AVCODEC_LIBRARIES=avcodec
-- AVCODEC_INCLUDE_DIRS=
--   - AVCODEC not found.
-- AVDEVICE_LIBRARIES=avdevice
-- AVDEVICE_INCLUDE_DIRS=
--   - AVDEVICE not found.
-- AVFORMAT_LIBRARIES=avformat
-- AVFORMAT_INCLUDE_DIRS=
--   - AVFORMAT not found.
-- AVUTIL_LIBRARIES=avutil
-- AVUTIL_INCLUDE_DIRS=
--   - AVUTIL not found.
-- POSTPROCESS_LIBRARIES=
-- POSTPROCESS_INCLUDE_DIRS=
--   - POSTPROCESS not found.
-- SWSCALE_LIBRARIES=swscale
-- SWSCALE_INCLUDE_DIRS=
--   - SWSCALE not found.
CMake Error at /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
  Could NOT find FFmpeg (missing: FFMPEG_INCLUDE_DIRS AVCODEC_INCLUDE_DIRS
  AVFORMAT_INCLUDE_DIRS AVUTIL_INCLUDE_DIRS AVDEVICE_INCLUDE_DIRS
  AVFILTER_INCLUDE_DIRS POSTPROC_INCLUDE_DIRS SWSCALE_INCLUDE_DIRS
  SWRESAMPLE_INCLUDE_DIRS)
Call Stack (most recent call first):
  /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:600 (_FPHSA_FAILURE_MESSAGE)
  CMakeModules/FindFFmpeg.cmake:165 (find_package_handle_standard_args)
  CMakeModules/Bootstrap_Linux.cmake:45 (FIND_PACKAGE)
  CMakeLists.txt:36 (INCLUDE)

With my patch the build works.

[Julusian]

thanks, both of these look sensible and don't break the ci builds so work fine on ubuntu still

perhaps I should add some more build tests based on different linux distros..