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Combining odd and even frames in Shake

I've just finished helping a guy with a Shake issue via email and I think the solution would be useful to others. He had a situation where he had one movie clip with all the odd frames from a sequence and another clip with all the even frames, and he wanted to combine them into a single file.

At first glance, it would appear to be as simple as using the Select node to switch between them, however you would miss out half of the frames by doing this. Here's the solution that worked for him:

1. Import the two files into Shake via the FileIn node.

2. Add a TimeX node to the first clip and set it to 0.5*time (this doubles every frame) and do the same for the second clip.

3. Add a Select node and plug the output of the two TimeX nodes into it. So that it's not confusing later on, make sure the output of clip 1 goes to the first input and clip 2 goes to the second.

4. In the Branch parameter of the Select node, set a keyframe at frame 1 with a value of 1 (i.e. the first input), then step to frame 2 and keyframe the value to 2 (the second input).

5. Load the parameter into the Curve Editor by clicking the clock icon next to the Branch field so that a tick icon appears, and then click the Curve Editor tab.

6. In the Curve Editor, change the Cycle parameter to MirrorValue.

7. When you render the FileOut, make sure to double the frame range as the sequence is now twice as long.