When I first bought the TinyTV 2, I assumed any AVI file would play, so I was just as surprised as you when most of my videos didn't work. I also try to keep my Mac secure by downloading only from the App Store, so I completely understand your hesitation. I experimented with a couple of well-reviewed converters from the store, but none of them produced the correct format. In the end, the only reliable method I found was using the official TinyTV Video Converter. It's not ideal, but it seems like the most straightforward solution right now.