av_log: print FFmpeg version

The individual library versionsd are pretty useless. This will actually
tell us at least the git hash or git tag of the FFmpeg build.

TOOLS/old-configure

@@ -786,6 +786,12 @@ api_statement_check \
     libavutil/frame.h \
     'enum AVFrameSideDataType type = AV_FRAME_DATA_SKIP_SAMPLES'
 
+api_statement_check \
+    "libavutil av_version_info()" \
+    HAVE_AV_VERSION_INFO \
+    libavutil/avutil.h \
+    'const char *x = av_version_info()'
+
 check_pkg_config "libavfilter" $_libavfilter LIBAVFILTER 'libavfilter >= 5.0.0'
 
 check_pkg_config "libavdevice" $_libavdevice LIBAVDEVICE 'libavdevice >= 55.0.0'

common/av_log.c

@@ -239,6 +239,10 @@ void print_libav_versions(struct mp_log *log, int v)
                 "expose subtle ABI compatibility issues\nand can lead to "
                 "misbehavior and crashes.\n", LIB_PREFIX);
     }
+
+#if HAVE_AV_VERSION_INFO
+    mp_msg(log, v, "%s version: %s\n", LIB_PREFIX, av_version_info());
+#endif
 }
 
 #undef V

wscript

@@ -437,6 +437,12 @@ FFmpeg/Libav libraries. You need at least {0}. Aborting.".format(libav_versions_
         'func': check_statement('libavutil/pixfmt.h',
                                 'int x = AV_PIX_FMT_MMAL',
                                 use='libav'),
+    }, {
+        'name': 'av-version-info',
+        'desc': 'libavtuil av_version_info()',
+        'func': check_statement('libavutil/avutil.h',
+                                'const char *x = av_version_info()',
+                                use='libav'),
     }
 ]