At this time Slatable only supports video shot in Slatable or the iPhone Camera app. You can also use Filmic Pro.
If you want to import video from other sources, such as DSLRs or video cameras, please test an Audition first.
If the app doesn't compile your files open them iMovie (on your Mac or iPhone) and then export them for Apple devices to use in Slatable.
We're planning on allowing importing from other video sources in a future major upgrade.