As for this kind of situation, you can resort to Leawo iTransfer to solve this problem. Just follow the below steps.
1. Run Leawo iTransfer on your computer and connect iPhone to computer with the USB cable. The software will recognize your iPhone and automatically detect the contents in your iPhone. Then the software will show the libraries of your iPhone in the left sidebar.
2. Click "Movies" in the left sidebar, and the contents will be shown in the right part of the window. If your Movie Library is empty, the software will offer an "Add File" button in the middle of the window to help you add video files from computer. Or you can click "File > Add > Add File/Add Folder" at the upper right corner of the window to add video files from your computer.
3. After choosing files, the software will start transferring videos from PC to iPhone. The progress bar in the dialog will show you the percentage of the transfer process, and when the transfer is done, you will get the videos in the target folder.
We all know that Apple has not enabled its iTunes to transfer video from iPhone to iTunes or computer. However, with Leawo iTransfer, you could easily transfer video from iPhone to computer or iTunes, as well as other data and file types like pictures, messages, notes, etc.
For more details, check: How to Transfer Videos from PC to iPhone