prevent multiple av_register_all()

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@3570 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/allformats.c

@@ -26,6 +26,12 @@
  */
 void av_register_all(void)
 {
+    static int inited = 0;
+    
+    if (inited != 0)
+        return;
+    inited = 1;
+
     avcodec_init();
     avcodec_register_all();