If you've made some speeches from time to time, you already know the case.
You've shown some videos during the presentation and then you share the exported PDF to someone that asked for it. The problem is that all those videos became black rectangles, at best.
We've already written about how PRESENTA allows to include (embed) videos from services such as Youtube and Vimeo.
There's an interesting side effect by using those services: the exported PDF will contain a poster-frame of the video as well as its URL, allowing the PDF readers accessing the videos quite easily.
Here a screenshot of a PDF exported from PRESENTA with embedded videos: