If you are looking how to get the cached files for videos with audio from the RC, I figured out how to do it.

-plug your controller into your computer. It won't show it's plugged in or give you an option to view the files yet.
-So what you do is on the settings page(not connected to the drone), swipe from the top down where it brings up volume and brightness.
-Once you connect the RC to your computer and have the volume screen pulled down, you should see a USB symbol in the top left hand corner. Click on it and it'll take you to "turn on USB sharing" so click turn on.
-After a few seconds, the drives should show up on your computer(normally under DJI).  
-You can go through and find the videos to transfer to your computer. To make it easier, find the video with audio you want to download on the P4P+ RC gallery and click details. It'll tell you where it's stored on the internal memory so you can find exactly which folder it's in without taking a long time. Hope this helps.

After looking and looking for hours, it didn't seem like there was any easy way to get the cached files off the remote since you couldn't transfer them to an SD card. I never once was able to find anyone mentioning turning on USB sharing on the RC to find it on your computer. I hope this is able to help a lot of people who have been looking for a way to get the audio from videos!

Very helpful!  My icons were in a little different place and I had to dig down to DJI...DJI.PILOT.PAD...VIDEOEDITOR...PRODUCTION...there I found 1280x720 MP4