If you want to add a video to a text editor, Click the

(Media) or

(Cosmos Vimeo Plug-in) icon to proceed.
(1) Click the 'audio/video file' icon.
(2) Copy/paste the YouTube content address to the 'Source URL' on the Link tab.
(3) Click the [Insert Media] button.
a movie file
When registering a video file that you own, you can register it in two ways:
(1) Click the 'audio/video file' icon.
(2) On the Link tab, click the [Browse repositories] button > locate and select the file in File Picker > Attachment.