Both audio and video are imported from mp4 clips. Audio on different tracks will mix, and the volume of each track or clip can be adjusted in several ways.
Verify that the slider for the audio track (at the left)
is fully to the right, and that the track or clip aren't muted.
Right-click the speaker icon the right-bottom of the Windows desktop and choose Volume Mixer. The VP volume slider should be maximum gain.
If still no sound or waveform on Mp4 clips, please share one or two. Follow these easy steps...
Upload the file/s to a free server, such as Google Drive or MS OneDrive, right-click the link and Share. Copy the result and paste it here or to me in a Private Message via the mail envelope in the top-right corner of this forum. When using Google Drive, if necessary change "restricted" to "anyone with link can view.**