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When ffmpeg use *-uninstalled.pc, configure fail #458

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@moi15moi

Currently, ffms2 attempts to link against ffmpeg to determine whether the -Wl,-Bsymbolic flag is required:

ffms2/configure.ac

Lines 105 to 146 in 6601f8c

AC_DEFUN([TEST_FFMPEG],
[AC_LINK_IFELSE([AC_LANG_PROGRAM([[
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
]],[[
avformat_network_init();
swscale_version();
]])], [eval $1=yes], [eval $1=no])
])
AC_MSG_CHECKING([whether FFmpeg works])
LIBS="$_LIBS $FFMPEG_LIBS"
TEST_FFMPEG([FFMPEG_WORKS])
AC_MSG_RESULT([$FFMPEG_WORKS])
if test "$FFMPEG_WORKS" = no; then
AC_MSG_FAILURE([cannot link with FFmpeg])
fi
src_core_libffms2_la_LDFLAGS=""
AC_MSG_CHECKING([whether -Wl,-Bsymbolic is needed])
if test "$enable_shared" = yes; then
_LDFLAGS="$LDFLAGS"
LDFLAGS="$LDFLAGS -shared $lt_prog_compiler_pic"
TEST_FFMPEG([no_bsymbolic])
if test "$no_bsymbolic" = "no"; then
LDFLAGS="$LDFLAGS -Wl,-Bsymbolic"
TEST_FFMPEG([bsymbolic])
if test "$bsymbolic" = "yes"; then
src_core_libffms2_la_LDFLAGS="$src_core_libffms2_la_LDFLAGS -Wl,-Bsymbolic"
else
AC_MSG_RESULT($bsymbolic)
AC_MSG_FAILURE([cannot build ffms2 as a shared library])
fi
else
bsymbolic=no
fi
LDFLAGS="$_LDFLAGS"
src_core_libffms2_la_LDFLAGS="$src_core_libffms2_la_LDFLAGS -version-info $VERSION_INFO"
else
bsymbolic=no
fi
AC_SUBST([src_core_libffms2_la_LDFLAGS])

ffmpeg documentation explains when this flag is necessary: https://ffmpeg.org/platform.html#Advanced-linking-configuration

The problem is that ffmpeg may not be available at configure time. For example when the user is relying on a *-uninstalled.pc (ex: libswresample-uninstalled.pc) file. In this situation, the current test will fail, making it impossible to build ffms2.

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