Constantly have to re-download

Why do I have to re-download every family movie I encrypt? 200MB etc file has to be dwnloaded every time I want to watch?

Well, the app accesses directly to the encrypted files stored in your cloud. And therefore the video has to be downloaded and decrypted by cryptomator first, to be viewed.
You can save the video as a local copy on your device via the “share” function after the first download, if you want to view it more often (to be honest, Im not on android, but as this function is available for iOS, I guess its available for android as well).
Please note that the local copy is not encrypted by cryptomator. (but maybe you have enabled local encryption of files by android)

On Android why do I have to re-download a video file every time to watch the file.

Feature request for caching:

Your downloaded video might be getting stored on cloud. That’s why you need to re-download it. It’s just like offline video. To avoid this issue you may simply download your video on your device through4hub

You can also try the Cryptomator for Android in version 1.5.0-beta1 which adds this feature (caching of downloaded files): First Beta of Cryptomator 1.5.0