ffmpeg: detect which ffmpeg headers should be included

Since ffmpeg svn r12865, you have to include libavcodec/avcodec.h
instead of avcodec.h.  This cannot be checked at compile time, instead
we have to add a check to configure.ac.  Viliam's original ffmpeg
plugin was based on the newer ffmpeg library, while my Debian
installation had the older version.  My attempt to correct his include
statements wasn't correct after all.

configure.ac

@@ -689,6 +689,17 @@ if test x$enable_ffmpeg = xyes; then
 		enable_ffmpeg=no)
 fi
 
+if test x$enable_ffmpeg = xyes; then
+	# prior to ffmpeg svn12865, you had to specify include files
+	# without path prefix
+	old_CPPCFLAGS=$CPPFLAGS
+	CPPFLAGS="$CPPFLAGS $FFMPEG_CFLAGS"
+	AC_CHECK_HEADER(libavcodec/avcodec.h,,
+		AC_DEFINE(OLD_FFMPEG_INCLUDES, 1,
+			[Define if avcodec.h instead of libavcodec/avcodec.h should be included]))
+	CPPCFLAGS=$old_CPPFLAGS
+fi
+
 AM_CONDITIONAL(HAVE_FFMPEG, test x$enable_ffmpeg = xyes)
 
 case $with_zeroconf in

src/inputPlugins/ffmpeg_plugin.c

@@ -29,9 +29,15 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
+#ifdef OLD_FFMPEG_INCLUDES
 #include <avcodec.h>
 #include <avformat.h>
 #include <avio.h>
+#else
+#include <libavcodec/avcodec.h>
+#include <libavformat/avformat.h>
+#include <libavformat/avio.h>
+#endif
 
 typedef struct {
 	int audioStream;