Samsung really need to sort this problem out for the S6 and S7 phones..i wasted practically all my evening trying to work out how to transfer video from my pc to my s7 edge. Smart switch seems to be a waste of time, no matter what i did nothing worked. Finally after searching google i managed to find a solution that does work..i'll copy and paste the article here.
Transfer with Windows Media Player
Step 1. Connect Samsung Galaxy S7/S7 Edge to PC with the USB cable that comes with the Galaxy S7/S7 Edge.
Step 2. Launch Windows Media Player on PC, and on the left side bar of Windows Media Player, you'll find the Galaxy S7/S7 Edge icon.
Step 3. Click on the "Sync" button in top right corner. Drag music, videos, and photos to the "Sync list" area. Here you can drag music, videos, and photos from both the Windows Media Library and your PC folders.
Step 4. When you have dragged all the music, video, and photo files you want to watch on the Galaxy S7/S7 Edge, click "Start sync."
Step 5. Move to the left side bar to click "Sync status" under your Galaxy S7/S7 Edge option to check whether the videos, music and photos have been copied and transferred to your Samsung Galaxy S7/S7 Edge.
If that helps anyone i wont feel like my night was wasted lol.