Webcast mode is a streaming delay to enable for your live events for a better attendee experience.
Webcast mode will help with attendees with a slow internet connection and will help with a larger audience, it adds a 30 second delay to the stream so everyone has the same smooth webinar experience.
Creating a Live Webinar, and enabling Webcast Mode in Advanced Settings (on your webinar's Edit page).
You will see three options :
Auto: This is automatically enable webcast mode for all attendees and presenters.
Required: Making it a requirement for all attendees to attend the webinar.
Optional: Allowing the attendee's to decide to opt in or out for webcast mode.
Currently it's a required setting for webinars with over 50 registrants