Use 64 bit for times in mpeg4_encode_gop_header()

contrib/sdk/sources/ffmpeg/ffmpeg-2.1/libavcodec/mpeg4videoenc.c

@@ -864,7 +864,7 @@ void ff_set_mpeg4_time(MpegEncContext * s){
 }
 
 static void mpeg4_encode_gop_header(MpegEncContext * s){
-    int hours, minutes, seconds;
+    int64_t hours, minutes, seconds;
     int64_t time;
 
     put_bits(&s->pb, 16, 0);