Index: libmpdemux/muxer_lavf.c
===================================================================
--- libmpdemux/muxer_lavf.c	(revision 26672)
+++ libmpdemux/muxer_lavf.c	(working copy)
@@ -87,6 +87,21 @@
 static offset_t mp_seek(URLContext *h, offset_t pos, int whence)
 {
 	muxer_t *muxer = (muxer_t*)h->priv_data;
+
+	/* Hack:
+	 * As of ffmpeg r13061, lavf tests seeking to determine if the output
+	 * is streamed. This leads to mp_seek() getting called before
+	 * h->priv_data is set. There's a circular dependency.
+	 * 1. avio.c:url_fopen() calls muxer_lavf.c:mp_seek()
+	 * 2. mp_seek() needs h->priv_data to be set
+	 * 3. ...but h doesn't exist before url_fopen() is called, so
+	 *    h->priv_data cannot be set until afterward
+	 * Returning 0 here nullifies lavf's streaming test, but at least it
+	 * avoids segfaulting.
+	 */
+	if (! muxer)
+		return 0;
+
 	if(whence == SEEK_CUR)
 	{
 		off_t cur = stream_tell(muxer->stream);