It's all about how the quality of the video, the relevance of the video to what the user expects / wants to have happen as part of their experience in that moment of the app.
Most of all, the video has to be as short as possible to convey it's meaning & message.
Finally, it has to create the right feeling for the user. Are they happier or better educated/informed or feeling a sense of accomplishment or feeling whatever feeling they're supposed (by your promises to the user) to be feeling?
We think about this quite a bit for HotelTonight, and especially considered it for a dating product I worked on in the past.
For retention the two things to think about are bringing the customer back for future visits and exposing them to additional content within the same visit.
One thought is to make the video episodic, if possible. If there is really great content that takes 10 minutes to explain, try to break that down into 3-5 parts. That way they 1) aren’t overwhelmed by a 10-minute video and 2) build a relationship with the content wanting more of it. Thus, coming back, or staying longer, to see the full series.
You can also make it episodic by creating follow up videos. For example, if the first video answers a question like "How do you boil an egg", the second video could answer other egg related questions.
Also, see if you can create video answers to questions people ask. So, if someone in the egg video asks how this might be different if you live in high altitude, follow up with a second video that explains how different environments might change the outcome.
Finally, build a recommendation engine within the product to broaden the content they are exposed to. Make it almost too easy to get caught up in a bunch of videos. Wikipedia does a great job of this. You may go on to just learn about Germany, but before long you’re researching the various projects of David Hasselhoff.
Hope this helps! Happy to jump on a call to build some ideas for your specific product.