I just tested this with one of my installations with the following results:
1. Create a new test LO using the main xot project template
2. Add a Misc > YouTube Video page
3. Add a Text > Plain Text page
4. Add embed code provided by YouTube to the Misc > YouTube Video page Embed Code panel. (I used the embed code via the sharing option for this video
www.youtube.com/watch?v=yVD_nSLINms )
5. Add the same embed code provide by YouTube to the Plain Text page by first switching to the Source View via the <> Source View button on the toolbar then pasting the embed code.
6. Publish and view to check both pages work online then export via both deployment zip and offline zip options.
7. Extract and test via Firefox
Results:
offline export both pages work
deployment export YouTube page doesn't work but Plain Text page does
Not seeing any changing/stripping of http/https? Perhaps that only happens if the xerte install is via https? Don't have time to test that right now but are there any other differences here?
HTH
Ron