The bandwidth of the encoding is too low for playing cryptographic games. This doesn't preclude faking a video by introducing the code into your faked video--it's just that that is much, much more difficult than stringing pieces together in an incorrect fashion.

This is more akin to spread spectrum approaches--you can perfectly well know the signal is there and yet finding it without knowing the key is difficult. That's why old GPS receivers took a long time to lock on--all the satellites are transmitting on top of each other, just with different keys and the signal is way below the noise floor. You apply the key for each satellite and see if you can decode something. These days it's much faster because it's done in parallel.