libx264: specify field for default union values in options

Fix warnings.

libavcodec/libx264.c

@@ -421,14 +421,14 @@ static av_cold int X264_init(AVCodecContext *avctx)
 #define VE AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_ENCODING_PARAM
 
 static const AVOption options[] = {
-    {"preset", "Set the encoding preset", OFFSET(preset), FF_OPT_TYPE_STRING, 0, 0, 0, VE},
-    {"tune", "Tune the encoding params", OFFSET(tune), FF_OPT_TYPE_STRING, 0, 0, 0, VE},
-    {"fastfirstpass", "Use fast settings when encoding first pass", OFFSET(fastfirstpass), FF_OPT_TYPE_INT, 1, 0, 1, VE},
-    {"profile", "Set profile restrictions", OFFSET(profile), FF_OPT_TYPE_STRING, 0, 0, 0, VE},
-    {"level", "Specify level (as defined by Annex A)", OFFSET(level), FF_OPT_TYPE_STRING, 0, 0, 0, VE},
-    {"passlogfile", "Filename for 2 pass stats", OFFSET(stats), FF_OPT_TYPE_STRING, 0, 0, 0, VE},
-    {"wpredp", "Weighted prediction for P-frames", OFFSET(weightp), FF_OPT_TYPE_STRING, 0, 0, 0, VE},
-    {"x264opts", "x264 options", OFFSET(x264opts), FF_OPT_TYPE_STRING, 0, 0, 0, VE},
+    {"preset", "Set the encoding preset", OFFSET(preset), FF_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},
+    {"tune", "Tune the encoding params", OFFSET(tune), FF_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},
+    {"fastfirstpass", "Use fast settings when encoding first pass", OFFSET(fastfirstpass), FF_OPT_TYPE_INT, {.dbl=1}, 0, 1, VE},
+    {"profile", "Set profile restrictions", OFFSET(profile), FF_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},
+    {"level", "Specify level (as defined by Annex A)", OFFSET(level), FF_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},
+    {"passlogfile", "Filename for 2 pass stats", OFFSET(stats), FF_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},
+    {"wpredp", "Weighted prediction for P-frames", OFFSET(weightp), FF_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},
+    {"x264opts", "x264 options", OFFSET(x264opts), FF_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},
     { NULL },
 };