The first thing you need to know is how to manipulate the Fractal Noise effect in After Effects, which is by far the most useful effect for creating animated backgrounds. To start off, create a new composition in the format of your choice (my examples below are in NTSC DV) and make its duration 5 seconds. Then add a new solid to your comp by choosing Layer > New > Solid, and in the Solid Settings dialog select Make Comp Size. It doesn’t matter what color it is, just go ahead and click OK. Then apply the Fractal Noise effect by choosing Effect > Noise & Grain > Fractal Noise and your comp will look like this:
 

Figure 1: A new comp with the Fractal Noise effect applied

Next, to animate the noise, set an initial keyframe for the Evolution property by clicking on its stopwatch icon in the Effect Controls panel. If you can’t see the Effect Controls panel, press the F3 key on your keyboard to reveal it.

Figure 2: The Effects Controls panel

Then, press the End key on your keyboard, which will bring your Current Time Indicator to the last frame on the timeline. Turn the Evolution dial in the Effect Controls clockwise two rotations, which will animate the noise two cycles over the duration of the comp. To preview the animation, choose Composition > Preview > RAM Preview.

Not too interesting, is it? Well, that’s just the starting point. By learning how to manipulate the controls in Fractal Noise, and then adding some complementary effects, you can achieve an incredibly wide range of looks. For starters, go back to the Effect Controls and pull down the Fractal Type menu at the very top of the effect. Try selecting each of the options and doing a RAM Preview to get an idea of the basic look of each. Once you’ve finished, select Dynamic Twist (which will look like image 3 in Figure 3, below).

Figure 3: Four different options for the Fractal Noise effect

Next, you’ll make the noise more abstract by lowering its complexity. In the Effect Controls panel, click on the setting for Complexity (the default is 6.0) and change it to 3.0 (image 2 in Figure 3, on page 2). Next, to stretch it out and make wavy lines, twirl down the Transform property in the Effect Controls by clicking on the triangle to the left of its name. Deselect Uniform Scaling, and set Scale Width to 600 (image 3 in Figure 3, on page 2) and Scale Height to 35 (image 4 in Figure 3, on page 2).

Now do a RAM Preview again to see the results. Quite different from where we started out, isn’t it? And the best part is the animation is the result of just two keyframes set on the Evolution property.

In order to make this more interesting, we’re going to apply three complementary effects: Levels, Fast Blur, and CC Toner. Levels (which works the same way as Levels in Adobe Photoshop®) will let us adjust the brightness and contrast with a great degree of control, Fast Blur will make the background more abstract, and CC Toner will let us colorize the final result.

First, apply Levels by choosing Effect > Color Correction > Levels. By moving the three triangles below the Histogram, you can adjust your black-and-white levels, as well as the gamma. Move the triangles so they’re about where I have them in Figure 4, below.

Figure 4: Move the sliders to adjust the black-and-white levels.

You can see the result is much different from the Fractal Noise effect by itself. Try playing with the sliders below the Histogram to see what kind of looks you can get, and then go back to the settings in the figure above.

Apply the Fast Blur effect by choosing Effect > Blur & Sharpen > Fast Blur. Set the Blur Dimensions to Horizontal, select Repeat Edge Pixels, and increase Blurriness to 300 by clicking and dragging on its value to the right, which will allow you to see the adjustment in the Composition Viewer as you make it.

Now add some color to your animation by choosing Effect > Color Correction > CC Toner. Click the color swatch for Midtones, and then select a vibrant blue color.

Figure 5: Add some color to your animation.

View the results

Finally, do a RAM Preview to see your finished animated background. Experiment by changing the Fractal Type, tweaking the Levels settings and blur amount, and mapping different colors in CC Toner.

Most of the Background Animation Presets in After Effects 7.0 use this formula, or a variant thereof. Since the Presets are just a stack of effects and keyframes, applying them and then “looking under the hood” to see how they were created is a good insight into how to create more varied backgrounds. A good keyboard shortcut is UU (press the letter U key on your keyboard twice in rapid succession), which shows you what properties on a layer have been modified from their default settings. By applying a Background Animation preset, pressing the F3 key to reveal its Effect Controls, and then using the UU keyboard shortcut, you can get a good overview of how the preset was constructed. To see how it was animated, press U on your keyboard to reveal on the timeline only the properties that have keyframes. The example I just took you through is very similar to the Red Speed Background Animation preset in After Effects 7.0.

If you create an animated background that you really like, save it as a preset for future use by dragging the effects and keyframes from the timeline to the Effects & Presets panel. You'll get a dialog asking you to name your new preset, and then it's yours to use again and again (or share with others).
 

Tutorial Source