If you are unsure that your video content is in the correct format for Foliobook please refer to Apple's help facilities to obtain the latest advice. Apple devices change over time and therefore its best to refer to the source for the latest information about this.
Because there can be considerable differences in how video content is encoded, I recommend a couple of tips can help you check that your videos are in an acceptable format for the iPad.
1) Use a rendering app to output to the desired device type.
Get a copy of the free Handbrake app for the Mac (if a Mac user). On Windows there are a number of free and proprietary converters which can do the same job.
Then use that app with one of the Apple presets to save a new version of your video file, for example with Handbrake you can choose an Apple TV preset or a preset for Apple devices and it will select an optimal format and settings.
Whichever tool you use, find a preset for generating video suitable for playing on an AppleTV. If it plays on AppleTV it is almost certainly compatible with the iPad and Foliobook.
2) Check that your video content plays in the native player on the iPad. If you can import the video and play it on the iPad, then its in an acceptable format to load into Foliobook.