The narrator is the one who has the knowledge and expertise as well. Ensures that the data will be necessary to listen to the narration. It is accurate and can be helpful to you.
The lecturer is someone with knowledge and expertise as well. Make sure that the information gets from listening to the narration is the correct information and can also cause benefits to you.
The keynote speaker is a person who has the knowledge and expertise to do a good, confident that the information that will be received, the commentary will be accurate information, and the ability to make a useful to you.