Comment to Enabling comments form to upload video
It's possible to enable video (or any other files) attachments in comments by executing the following query and clearing cache in Studio > Dashboard:
UPDATE `sys_objects_storage` SET `ext_allow` = 'jpg,jpeg,jpe,gif,png,mp4,mov,mpg,avi,webm,mkv' WHERE `object` = 'sys_cmts_images';