It is 2016 as I'm writing this but I wanted to share how I transfer MP4s to my macbook from a mini external SD card. The icon for the SD card drive shows up on the desktop. When I open files I can see Jpegs readily but I don't see any of the MP4 files.
I discovered two ways to get them onto my desktop and from there to wherever.
1. If you have the Photos program you simply open it, go to File and scroll down until you see Import. Click on that and it will bring up all the folders and every file type in them. From there you can grab as many MP4s as you like and drag and drop them wherever you like. You can also import them into the Photos program, if you want to save them there, and then drag and drop them onto your desktop.
2. Open Finder and click on Applications. Find Quicktime Player and click on that. From there you will find all your MP4s and you can drag and drop them anywhere you like. No need to open the iMovie program unless you want to immediately edit a new movie file.
You take this same idea for PDFs. Just open up the Preview program in Applications and drag and drop wherever you like. I hope this helps someone. 🙂