When running totem this warning can be seen:

(totem:14134): GLib-GIO-CRITICAL **: g_file_new_for_path: assertion 'path != NULL' failed

It seems to be caused by XDG_VIDEOS_DIR being unset on my system and the "save-file" totem plugin not handling the g_get_user_special_dir call returning NULL properly in two places.


totem-3.13.92$ grep -A 2 g_get_user_special_dir src/plugins/save-file/*
src/plugins/save-file/totem-save-file.c:		dest_path = g_build_filename (g_get_user_special_dir (G_USER_DIRECTORY_VIDEOS), filename, NULL);
src/plugins/save-file/totem-save-file.c-		dest_uri = g_filename_to_uri (dest_path, NULL, NULL);
src/plugins/save-file/totem-save-file.c-		g_free (dest_path);
--
src/plugins/save-file/totem-save-file.c:	videos_dir = g_file_new_for_path (g_get_user_special_dir (G_USER_DIRECTORY_VIDEOS));
src/plugins/save-file/totem-save-file.c-	if (file_has_ancestor (file, videos_dir)) {
src/plugins/save-file/totem-save-file.c-		g_debug ("Not enabling offline save, as '%s' already in ~/Videos", mrl);

(Also notice the hard-coded path in the debug output could be changed to use %s and videos_dir to say the correct directory.)