diff --git a/doc/todo/switch_from_quvi_to_youtube-dl.mdwn b/doc/todo/switch_from_quvi_to_youtube-dl.mdwn
index 145d61a33d..aa2f6955d1 100644
--- a/doc/todo/switch_from_quvi_to_youtube-dl.mdwn
+++ b/doc/todo/switch_from_quvi_to_youtube-dl.mdwn
@@ -50,3 +50,10 @@ And --get-filename does not report the actual filename when that happens.
 This seems to be due to format merging by ffmpeg; with -f best, it does
 not merge and so does not do that.
 <https://github.com/rg3/youtube-dl/issues/14864>
+
+To do disk free space checking will need a different technique than
+git-annex normally uses, because youtube-dl does not provide an easy way to
+query for size. Could use --dump-json, but that would require downloading
+the web page yet again, so too expensive.. and, the json seems to have
+"filesize: null" for youtube videos. What does work is the --max-filesize
+option, which makes youtube-dl abort if it's too big.