I've an android app already developed.
The android app is essentially a wrapper around a HTML5 web app.
We use HTML5 offline caching to provide the ability to play when disconnected from the internet.
Chrome/Firefox on the desktop will cache the video and images however Android devices appear to selectively ignore video in the cache manifest which prevents the video from being stored locally on the device.
It's understandable that Android would ignore caching video to keep the storage use to a minimum on mobile devices but we need a way around this.