Transfer video files from iphone to ipad?

If you mean transferring data between iOS devices, then this tutorial could help: https://bit.ly/2X7qtAR

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After syncing to iPad, you can transfer you data, if however you unable to transfer, you can try iPad file transfer tool. it will absolutely help you to transfer files safely.

If you download/rent/purchase those movies on your iPhone from the iTunes Store, you can just use the same Apple ID on your iPad to redownload those movies on your iPad. You can download rented movies to one device at a time during the rental period.
Another way is to use a data transfer program. Here's how to transfer data between two iOS device. All you need is two USB(lightning) cables and you can directly transfer your movies from your iPhone to your iPad.
Leawo iTransfer User Guide How to Transfer Files from iPad to iPhone

The most effective way to transfer video files from your iPhone to iPad, what you need is to launch a professional software like MobiKin Transfer for Mobile tool, and connect the devices to the computer by the USB cable. After doing these steps, you can choose the videos files as you like, and the software will begin to transfer, you just need to spend a little time to do, then you can finish this thing easily.
MobiKin Transfer for Mobile Mac Version

Here, this iPhone to iPad data transfer program is highly recommended to help you transfer files, such as contacts, SMS, video, photos, apps, music, books, etc. from iPhone to iPad.
Transfer Music Videos Contacts Photos from iPhone to iPad

After syncing to iPad, you can transfer you data, if however you unable to transfer, you can try iPad file transfer tool. it will absolutely help you to transfer files safely.

ITunes cant do this, you can use this software: IOS Transfer it's free to try.

Connect to iTunes and transfer them.