Here's a possible setup:
+ Effectlist: Input-Replace, Output-Ignore
- Interleave
- Buffer Save -> Save to Buffer 1
(outside effect list):
Dynamic movement: gridsize 1x1, check 'no movement (blend only)', specify Buffer 1 as source, and then write code that gives the variable 'alpha' a value between 0 and 1.
What happens is that AVS will make a copy of the current image before the preset, move into the effect list, apply the Interleave, and store the result in Buffer 1. Then, the dynamic movement (which we'll only be using as a dynamic blend) will blend between the normal image and the one in buffer 1. Alpha will specify how much buffer 1 is blended onto the original.
You'll need to learn how to write AVS code though. If you've done any kind of programming, it should be easy, and even without that, it shouldn't be too hard. Good knowledge of maths is a plus, because that's the basis for all the effects.
Here's an example piece of code for the blend (just paste these pieces of code in the appropriate box):
Init:
bv=0; bt=0;
Frame:
bv=bv * 0.9 + bt * 0.1;
OnBeat:
bt=1 - bt;
Point:
alpha=bv
This'll probably look weird at first. First, we set the custom variables (i.e. AVS doesn't assign any meaning to them) bv and bt, blend-value and blend-target, both to zero.
For every point, we use bv's value and use it as alpha-value.
Every beat, bt is given the value (1 - bt) instead. So if bt starts out zero, that means it'll alternate between one and zero every beat.
Now, every frame, we apply the formula above. This means that we assign 'bv' 90% of the original value, and 10% of the bt value. That's just a nice way of doing a transition from one value to a target value. So, every beat, the target value bt changes, and bv will change slowly to adjust, giving you a nice blend from non-interleaved to interleaved.