Fix building with newer FFmpeg

Index: src/osgPlugins/ffmpeg/FFmpegHeaders.hpp
--- src/osgPlugins/ffmpeg/FFmpegHeaders.hpp.orig
+++ src/osgPlugins/ffmpeg/FFmpegHeaders.hpp
@@ -5,7 +5,6 @@
 
 extern "C"
 {
-#define FF_API_OLD_SAMPLE_FMT 0
 #include <errno.h>    // for error codes defined in avformat.h
 #include <stdint.h>
 #include <libavcodec/avcodec.h>
@@ -44,19 +43,10 @@ extern "C"
 #endif
 
 #include <libavutil/mathematics.h>
+#include <libavutil/imgutils.h>
 
 #ifdef USE_SWSCALE
     #include <libswscale/swscale.h>
-#endif
-
-#if LIBAVUTIL_VERSION_INT <  AV_VERSION_INT(50,38,0)
-#define AV_SAMPLE_FMT_NONE SAMPLE_FMT_NONE
-#define AV_SAMPLE_FMT_U8   SAMPLE_FMT_U8
-#define AV_SAMPLE_FMT_S16  SAMPLE_FMT_S16
-#define AV_SAMPLE_FMT_S32  SAMPLE_FMT_S32
-#define AV_SAMPLE_FMT_FLT  SAMPLE_FMT_FLT
-#define AV_SAMPLE_FMT_DBL  SAMPLE_FMT_DBL
-#define AV_SAMPLE_FMT_NB   SAMPLE_FMT_NB
 #endif
 
 }
