Hi Russell
FLV is Flash video and that is probably the issue. Only flash based video players can play it back. Moodle can provide a flash player for you on desktop machines, thats why it works there. But not for mobile devices.
So the best advice I can give is to convert all your flv videos to html5 player friendly mp4 files. There is lots of software out there that can do this, perhaps look at something called handbrake.
