Keep music underneath the explanation
Narration should remain easy to understand.
Prepare
Choose music with a pace and texture suited to the subject. A busy lead instrument can mask speech even at a modest level. Start with the narration alone, then add music gradually while listening to consonants and quiet phrases.
Work through the decision
Listen through transitions and pauses. Music that feels comfortable during speech can jump forward when the voice stops. Use the available audio controls to avoid abrupt entrances and endings.
Review the result
Review with headphones and a small speaker at a moderate volume. If you need to strain to hear the words, simplify the music choice or lower it. Keep music provenance alongside the video assets.