fixing pipe seek bug

Originally committed as revision 3730 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/file.c

@@ -107,6 +107,7 @@ static int pipe_open(URLContext *h, const char *filename, int flags)
     setmode(fd, O_BINARY);
 #endif
     h->priv_data = (void *)(size_t)fd;
+    h->is_streamed = 1;
     return 0;
 }
 

libavformat/utils.c

@@ -1617,7 +1617,7 @@ static void av_estimate_timings(AVFormatContext *ic)
     }
     ic->file_size = file_size;
 
-    if (ic->iformat == &mpegps_demux) {
+    if (ic->iformat == &mpegps_demux && file_size && !ic->pb.is_streamed) {
         /* get accurate estimate from the PTSes */
         av_estimate_timings_from_pts(ic);
     } else if (av_has_timings(ic)) {