Currently youtube-dl produces broken filenames (of the form _-[videoid]). It seems something changed that breaks the metadata extraction, there've been some related changes upstream: https://github.com/ytdl-org/youtube-dl/issues/21934 https://github.com/ytdl-org/youtube-dl/commit/8dbf751aa241475dd8a7a6d3040713b5874fd057 Bumping to the latest version (2019.07.30) should fix this.
commit da0b9f2a69c0dccaef58d066a9fa13216d6b12fa Author: Jeroen Roovers <jer@gentoo.org> Date: Tue Aug 6 07:43:05 2019 +0200 net-misc/youtube-dl: Version 2019.08.02 Package-Manager: Portage-2.3.69, Repoman-2.3.16 Signed-off-by: Jeroen Roovers <jer@gentoo.org>