SOLVED! How to disable an app without access to the GUI?
update oc_appconfig set configvalue="no" WHERE appid="files_videoplayer" AND configkey="enabled";
manually changed via phpMyAdmin and OC is back online. hope that helps others.
also turns out i’ve not been reading the upgrade requirement docs (https://doc.owncloud.com/server/admin_manual/maintenance/manual_upgrade.html#preparation) so one to take note of for the future.