I fixed the bug mentioned in this report (the error message should be gone now and you should be able to search for mimetypes with PackageKit again). However, it could be possible that the error described here was masking another issue with missing codecs itself (I can't test that at time).
In any case, you can test this by upgrading PackageKit to version 1.1.7-1 (currently in Debian, maybe synced to Ubuntu), or by applying https://github.com/hughsie/PackageKit/commit/5e8a20440ca53080d5409a10f211a0979545816f ** Changed in: packagekit (Ubuntu) Status: In Progress => Fix Committed -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to packagekit in Ubuntu. https://bugs.launchpad.net/bugs/1719077 Title: Unable to find codecs to play videos Status in Grilo Plugins: Unknown Status in packagekit package in Ubuntu: Fix Committed Bug description: To reproduce: 1. Open Totem 2. Go to Channels and select The Guardian Videos 3. Select any video 4. Totem complains about missing codecs 5. GNOME Software then complains that app-install-data is missing See screenshots. ProblemType: Bug DistroRelease: Ubuntu 17.10 Package: ubuntu-software 3.26.0-0ubuntu2 ProcVersionSignature: Ubuntu 4.13.0-11.12-generic 4.13.1 Uname: Linux 4.13.0-11-generic x86_64 ApportVersion: 2.20.7-0ubuntu1 Architecture: amd64 CurrentDesktop: ubuntu:GNOME Date: Sat Sep 23 11:54:53 2017 InstallationDate: Installed on 2017-09-21 (2 days ago) InstallationMedia: Ubuntu 17.10 "Artful Aardvark" - Alpha amd64 (20170919) InstalledPlugins: gnome-software-plugin-flatpak N/A gnome-software-plugin-limba N/A gnome-software-plugin-snap 3.26.0-0ubuntu2 PackageArchitecture: all SourcePackage: gnome-software UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/grilo-plugins/+bug/1719077/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp