Wondershare Filmora: How to Mute Video Tracks
Just a quick guide on something that'd been bugging me forever. This works for your main video track and the "PIP" (picture-in-picture) tracks. Just turn the decibels down to -60 in the Audio Mixer.
To mute the video tracks, you'll have to just click the eye icons to the left of them. It will also make these tracks invisible, though (including when exporting). So reselect them if you want them to be visible.