A program for Windows 10 to turn photos and videos into a birthday clip
At the time of writing (Sep 2020), it looks like Video Editor does not provide &quot;audio ducking&quot; for videos with audio. As a workaround, you could use Custom audio (button next to Background music) and trim the music around video clips. From this thread on Microsoft Community:

The Video Editor does not currently have an audio ducking feature as you describe. Here are two potential workarounds:

Make the background music quieter throughout so your speaking can be heard
Use Custom Audio to add the same piece of music several times. You can trim very precisely by selecting a card on the storyboard to move your playhead, and then back in Custom Audio, drag the music trim handle to snap to the playhead location. Once you have the music in segments you can control the volume of each individually.



Unfortunately, if you have hundreds of clips, this may be very tedious work.