fix overhead and bitrate statistics

Originally committed as revision 8732 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -915,6 +915,8 @@ static void print_report(AVFormatContext **output_files,
 
     oc = output_files[0];
 
+    total_size = url_fsize(&oc->pb);
+    if(total_size<0) // FIXME improve url_fsize() so it works with non seekable output too
         total_size= url_ftell(&oc->pb);
 
     buf[0] = '\0';