Recording Screen With Quicktime and Video Cuts Short?

Hey all,

I'm new to Mac and Quicktime.

Here's what's happening...

1. I record the screen to make a screen recording video where the video is around 15-20 minutes long.

2. I finish the video and then get to preview it only to find about 75% of it is missing?

One video I created got the full length but half way through it I have a black screen which is missing about 3 minutes of recording. I can hear audio fine but all I have is black screen then comes back after 3 minutes or so.

This is very frustrating as you can imagine. I've been trying to create videos for the past 2 days and looked it up only to find unanswered questions.

Can someone please help?