You can use AutoPlay to help you. It can help you download camera roll videos to computer.
Step 1. Connect your iPhone to computer, the AutoPlay will appear automatically.
Step 2. Click on Import pictures and videos or Open device to view files.
If you click on "Import pictures and videos", AutoPlay will import all camera roll photos and videos. If you choose "Open device to view files", you need to find the videos that saved in different folders.