Unlike other design tools and word processors, After Effects does not have native text highlighting built in. I have some theories as to why this might be, but luckily highlighting text in After Effects is still possible.
I’ll show you how to do this manually, as well as how to automate this with Type – a Script UI that unlocks a ton of missing text functions in After Effects, including highlight.
With your After Effects comp open, select the Pen Tool (G).
Add a point to the beginning of your text. Then, holding shift to keep the line perfectly straight, add a second point to the end of your text.
In the timeline drag the stroke layer beneath the text layer, so that the text is fully visible.
Now you can remove the fill and change the stroke color to whatever you want.
Next adjust the stroke width so that it matches the size of your text.
You may need to reposition the stroke or shift the points of the path.
To animate the highlight, twirl down on the stroke layer and select Add > Trim Paths. Next, twirl down the Trim Paths and add 2 keyframes to the End value, animating from 0 to 100. Now the highlight will animate being drawn on. You can adjust the timing and easing of the keyframes however you like.
Type lets you automate the previous steps instantly with more precision.
To highlight text with Type, select the layer or the specific text range you want. Then click the highlight button.
Type will automatically create a stroke behind your text layer, that perfectly highlights the text selected.
You can animate the highlight in by holding shift while clicking the highlight button. This will add trim path keyframes which you can freely adjust.
Since the highlight is a stroke, you can change the color, stroke width, or the path itself as you would any other path in After Effects.
By default a highlight will be 100% of the cap height of your text. And will be trimmed to the exact sides of the text. You can change these defaults under Settings > Markup > Highlight. Here you can also change the default color of your highlight. The color default can also be quickly changed by holding Option while clicking the highlight button.
With Type, highlighting text in After Effects has never been easier.