The following process covers the steps to get After Effects to dissolve or blend from one scene to another. For instance, how you could combine three scenes of a treadmill walk sequence, to make a longer, overall scene.
In After Effects, make your Main Composition long enough to accommodate three panning backgrounds, including overlapping transitions. For example:
- Scene/Background 1 = 5 seconds or 120 frames
- Scene/Background 2 = 5 seconds or 120 frames
- Scene/Background 3 = 5 seconds or 120 frames
Add those together, and you will get 15 seconds or 360 frames. However, you’ll also dissolve in between each background, which will mean that you’ll require less than 15 seconds. Let’s not worry about that yet. It would be easier to make a composition with more than enough duration, and then trim back later.
You will need to include black at the beginning and end of the combined animation sequence, so you should add at least 3 seconds of black at the head of the animation sequence, and at the tail (but, more about this in a moment):
- Introductory black screen = 3 seconds or 72 frames
- Combined animation scenes = Approximately 360 frames (for now, at least)
- Concluding black screen = 3 seconds or 72 frames
Let’s create a Main Composition that is 500 frames in length (go to the Main Menu and choose Composition > Composition Settings and enter 500 frames for duration).
You should also create panning backgrounds in their own compositions. That is, create the animation for each scene in its own composition. In each comp, you should include the “looping” treadmill character, and any panning background and foreground material you would like to include in the scene.
Each scene/composition should include the tempo of the pan, so that it moves behind a treadmill character at the correct rate and does not make it look as though the character’s feet slip.
- The tempo of the pan depends on the rate of the walking character.
- If you’ve placed the treadmill character against a panning background and the background appears to move too fast (and the character’s feet slip as a result), you will have to move the keyframes further apart, so that it takes longer for the background to pass by.
- If the background moves too slowly (and the character’s feet slip), you will have to adjust the position of the artwork, so that it doesn’t travel as far, between Position keyframes.
After you’ve arrived at the right timing for each scene, you’re almost ready to place them in a Master Scene, or Master Composition. In that Comp, you can add dissolves, to make the character walks through three locations over a longer passage of time.
We’ll use an effect that will create simple transitions between each scene. But, to make the sequence look even better, you should fade up from the opening scene/composition, and fade down from the final scene.
To do so, make a black solid (referring to the Main Menu, go to Layer > New > Solid. From the Solid Setting, go to Colour and choose Black — and select “Make Comp Size).
Bring the Black Solid into the Main Composition Timeline, as the first layer.
If you plan to produce an overall sequence that begins with 3 seconds of black, you’ll not only have to change the duration of the solid, but you will have to include another second to overlap in the dissolve. So click on the layer, select the right-hand edge of the solid (or its “out point”), drag the edge to the right, and make it 96 frames or 4 seconds in duration (or longer if you wish).
Then, go ahead and place the three Comps (Scenes 1, 2 and 3) in the Main Composition Timeline. Place them in order, on top of each other, but don’t spread them out in the Timeline yet. We’ll do that in a moment.
Finally, you should add black for the end of the overall sequence. A quick way to do so would be to select the introductory black in the Timeline (on the top layer), duplicate it (Edit > Duplicate) and then drag the duplicated layer down so that it sits immediately below the third scene/composition in the Timeline).
From the Main Composition Timeline, click on the top black solid layer, hold down the shift key, and select the others (i.e., “select all” — introductory black solid, Scenes 1 to 3, and the concluding black solid).
Referring to the Main Menu, go to Animation > Keyframe Assistant > Sequence Layers.
From the Sequence Layers dialogue box, enter the following:
- Select “Overlap” (click the check box).
- Duration: choose something like 24 for a second-long transition (18 and 36 are also good amounts).
- Transition: From the pull-down menu, choose “Cross Dissolve Front and Back Layers”
- Press OK.
In this process, After Effects sets Opacity keyframes between the overlapping layers, so that, as one layer changes opacity from 100% to 0%, the other shifts from 0% to 100%. The resulting effect is a dissolve, from one layer to the next.
Finally, after you’ve completed these steps, you’ll probably find that your Main Composition is longer than you require. You can then trim the comp, to make it the correct duration, before you export a final movie:
- Adjust the Work Area Bar, so that it selects the true duration of the project.
- Go to the Main Menu and choose Composition > Trim Comp to Work Area.
- Doing so will trim off the unused portion of the Main Composition.