Imagine you have to make an animation where you want to show that a character is dreaming something. Let's get creative and say, in addition, that the subject is about to wake up and everything in the dream gradually fades away until it disappears completely. How would you accomplish this effect?
Well, let's start by saying that first, you should have two scenarios at the same time: one where the main character appears and another that shows the dream gradually disappearing. Let's focus on the latter scenario because, to achieve this trick, you must know how to fade out a specific part of a video in After Effects.
Working with two backgrounds to mask a single layer
To understand the concept behind working with two scenarios so you can choose only a part of one of them while leaving the rest of the image of the second footage visible, it is necessary to create two solid backgrounds of different colors.
To do that, simultaneously click Ctrl + Y or Cmd Y, choose a color, and hit Ok. Then, repeat the process one more time to create the second solid.
If one background completely overlaps the other, change the order in which their layers appear on the Timeline, so the second solid is below the first one. After doing so, move both solids so that each one occupies one-half of the canvas.
How to mask a specific part of a video to fade it out
Now that you have two backdrops visible on your composition screen, draw a Mask on the first solid you created:
- Activate the Pen Tool by clicking G, and start dotting until you create a custom shape. Don't panic if the rest of your background disappears, that's the point.
- Go to the Timeline and open the properties of the layer linked to the mask you just drew. Click on the 'Mask' tab and then on 'Mask 1'.
- Place the Time Indicator at the beginning of the Timeline and turn on the stopwatch next to the Mask Feather option.
- Move the Time Indicator again a few seconds forward on the Timeline, and in the same Mask Feather option, increase the pixels of the values highlighted in blue to smooth the edges of your mask progressively.
- Go back to the beginning of the Timeline with the Time Indicator once more, and this time turn on the stopwatch next to the Mask Opacity option. This is the most crucial step to fade out the part of your selected background.
- Move the Time Indicator a few seconds forward on the Timeline to create the second keyframe linked to the fading effect. In the same Mask Opacity option, decrease the percentage highlighted in blue to zero.
- Hit the spacebar to play and see how your masked backdrop fades away.
Play with the different transformation options that appear in your layer’s properties, so you can see how, by placing several keyframes on the Timeline, you can create multiple effects.
Once you have mastered this logic, you are ready to move on to a more professional level in motion graphics and After Effects.