[README.md] Document the 'duration' field in the output template (#6929)

diff --git a/README.md b/README.md
index 2ed75179182c93cfe7df8c584c7c17163cdb10ed..80152071d279954aca37361ce5b7286be57236cf 100644 (file)
--- a/README.md
+++ b/README.md
@@ -281,6 +281,7 @@ The `-o` option allows users to indicate a template for the output file names. T
  - `playlist`: The sequence will be replaced by the name or the id of the playlist that contains the video.
  - `playlist_index`: The sequence will be replaced by the index of the video in the playlist padded with leading zeros according to the total length of the playlist.
  - `format_id`: The sequence will be replaced by the format code specified by `--format`.
+ - `duration`: The sequence will be replaced by the length of the video in seconds.
 
 The current default template is `%(title)s-%(id)s.%(ext)s`.