multifilesink: document unit of "max-file-duration" property
diff --git a/gst/multifile/gstmultifilesink.c b/gst/multifile/gstmultifilesink.c
index 6cfc457..d2a55ef 100644
--- a/gst/multifile/gstmultifilesink.c
+++ b/gst/multifile/gstmultifilesink.c
@@ -285,8 +285,8 @@
    */
   g_object_class_install_property (gobject_class, PROP_MAX_FILE_DURATION,
       g_param_spec_uint64 ("max-file-duration", "Maximum File Duration",
-          "Maximum file duration before starting a new file in max-size mode",
-          0, G_MAXUINT64, DEFAULT_MAX_FILE_DURATION,
+          "Maximum file duration before starting a new file in max-size mode "
+          "(in nanoseconds)", 0, G_MAXUINT64, DEFAULT_MAX_FILE_DURATION,
           G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
 
   /**