My guess would be to have something like this
[normal frame 1]
[normal frame 2]
[something frame 1]
[something frame 2]
etc
etc
However, if that doesn't work, just experiment with it or skip over castform.
[normal frame 1]
[normal frame 2]
[something frame 1]
[something frame 2]
etc
etc
However, if that doesn't work, just experiment with it or skip over castform.