I ran across goofwear's tool to extract videos and photos from Samsung Motion Photos and thought it was useful. But I really wanted something that I'd be able to throw a whole album of motion photos at, rather than doing one at a time with this or the share app. I looked at the .bat file they used and implemented the same technique in C, so it could quickly process many photos. It's written with some direct Win32 API calls, so it's pretty much Windows only though making a cross platform command line version without the open dialog would be trivial. It is a simple program though, so it should work fine on Linux or Mac through Wine.
Here's the exe.
And here's the source code. It's a bit spaghetti. I wrote it rather quickly.
How to use:
1. Copy your Motion Photos off your Samsung phone, to your PC. Just copy them out of the DCIM folder.
2. Run the program. An "open" dialog appears. Apart from that there's no GUI on this program.
3. Browse to your photos and select them. Hold ctrl to select more than one, or shift to select a range. Or, ctrl+A to select all in a folder.
4. Click Open.
5. Wait. Depending how many you selected, it might take a little bit. When it's done, a message box will appear.
6. You should see *_photo.jpg and *_video.mp4 files next to the originals in the source directory. Note that this program does not modify the original files. It doesn't even open them with write permissions enabled.
Alternately, drag one or more photos from Windows Explorer onto the exe's icon instead of using the open dialog.