This is exactly the same premise as TrueCrypt. Nobody can know if there's anything on a TrueCrypt volume or not. They address the coercion (either by law enfo

This is exactly the same premise as TrueCrypt. Nobody can know if there's anything on a TrueCrypt volume or not. They address the coercion (either by law enforcement or guy with a gun), by allowing you to make hidden volumes inside the main volume. You open the main volume, filled with data you don't care about, and they never know that a hidden volume resides deeper. I see no reason that this same technique wouldn't work here. You record some boring video on the main volume, and record your main video on a hidden volume.