Deal with newer FFmpeg API.

Index: Core/HW/SimpleAudioDec.cpp
--- Core/HW/SimpleAudioDec.cpp.orig
+++ Core/HW/SimpleAudioDec.cpp
@@ -28,6 +28,7 @@
 #ifdef USE_FFMPEG
 
 extern "C" {
+#include "libavcodec/avcodec.h"
 #include "libavformat/avformat.h"
 #include "libswresample/swresample.h"
 #include "libavutil/samplefmt.h"
