This functions more or less identically to using a media out value, but the
desired speed is preserved through block length changes, even if the block's
length is reduced to zero (i.e. no rounding errors).
Since all NodeInputs will generally only need their data type and default
value set once, we place it all into the constructor for cleaner and easier
to manage code.
Like the base "Block" type, the "Transition" type will not be a node used on its
own, it will have to be derived. This type defines some basic behavior for a
transition (e.g. how much it overlaps its "from" and "to" blocks).
itsmattkc