http://devel.mplayer2.org/ticket/163
http://devel.mplayer2.org/changeset/8cd71527ade21ea27ea24cdcc66dc71dca460f85/

Index: stream/stream_vstream.c
===================================================================
--- stream/stream_vstream.c	(revision 1888e57af7e1ce51517ad9bdc2d201eaf84a98d2)
+++ stream/stream_vstream.c	(revision 8cd71527ade21ea27ea24cdcc66dc71dca460f85)
@@ -57,5 +57,5 @@
     vsnprintf(buf, 1024, format, va);
     va_end(va);
-    mp_msg(MSGT_STREAM, MSGL_ERR, buf);
+    mp_msg(MSGT_STREAM, MSGL_ERR, "%s", buf);
 }