Making an Audio visualizer template?

The bad news is: there is no way to "grab" the audio of a clip in FCPX from a Motion Template. You have to create every "visualizer" as an independent Motion project (or use the same project and make changes to the project as you go — it's not like each one is reusable.)

You could create a (recommended) generator in which you could import the audio and create the graphics and apply Audio behaviors for what you need to animate. Save the finished work as a generator and match the audio in FCPX to the generator.

There are a few problems with this method. Every time you save the generator, it will be as long as the audio is in the project. You cannot shorten the generator and you cannot stretch it out in FCPX to match time.

I have an idea for an easier way.

You can use FCPX, or Logic and get a snapshot (screen capture) of the audio waveforms. Images can be stretched out over time. I have an effect that will draw a line at the current point of the audio as long as the time of the image matches the length of the audio in FCPX (which is easy enough to do). The line marking the current location of the audio automatically adapts to any length. Something like:

You can colorize the waveform easily enough and you can use an Effect Mask > Color Mask to limit which color the bar appears in (as in this example — otherwise it goes from top to bottom). The bar's width, color and blend mode can be customized.

Just match the length of time you have the image in your storyline to the *audio track* length. Then add my effect to the waveform image. (It will work with any aspect ratio [width/height] up to 10:1).

This would be my recommendation for the most efficient way to represent the audio.