I am loosely copying this from my thread on the Steam forum for Vegas Movie Studio 13 Platinum as it is completely inactive and will hopefully shed more light on here.

When importing a video that has been recorded by Mirillis Action under the container MP4 the audio peak building just ends at 50% and finishes, so then on the timeline, the peaks are perfect until half way where they just stop and is completely silent for the rest of the way (visually on the peaks, and also during playback).

Exactly halfway during playback on all media software, there is a tiny stutter that skips a few frames and that is exactly where MS loses peaks and audio - So this points to Action doing something MS doesn't like.

• Version is: 13.0 (Build 982)
• Screenshot: http://prnt.sc/elbzih
• Audio continues playing just fine past the stutter on VLC media player.
• Re-formatting the audio via FFmpeg works (using "-acodec copy"), but it's annoying to have to do that due to the way it can take quite a while on hour long recordings.
• Isn't affected by Action's Hardware Acceleration.
• Happens on videos of any length (tested from above an hour down to below 5 seconds)
• Does not happen in an AVI container.

From what I can remember this started happening right as I upgraded my GPU to a GTX 1060.