You can use a custom stage to have applicants watch a video or complete some type of task, and then click a link ([PORTAL_LINK] or [PORTAL_URL] merge key), when they have finished. This then automatically moves the applicant to the next stage.
For example, you could embed a video in the Applicant Portal and then instruct applicants to watch the video.
Then, you could add a "Please click here after you watch the video" link with the URL set as the [ADVANCE_URL] merge key.
The action of clicking that link will take applicants to the next stage of the workflow if you have the 'Advance by completing an action' setting enabled.