Dynamic Text Box in After Effects

How to create a dynamic text box?

1. 1. Create a text layer and rename it to textLayer.
   2. Create a rectangular shape.
   3. Alt-click on the Size property and paste the expression below.

// edit horizontal padding in pixels

var horizontalPadding = 100;

// edit vertical padding in pixels

var verticalPadding = 50;

// text layer

var textLayer = thisComp.layer("textLayer");

// bounding box around text
var bbox = textLayer.sourceRectAtTime(time,true);
// box’s width + padding
[bbox.width * textLayer.scale[0] / 100,
bbox.height * textLayer.scale[1] / 100] +
[horizontalPadding, verticalPadding]

var textLayer = thisComp.layer("textLayer");

var box = textLayer.sourceRectAtTime(time, false);

textLayer.position - textLayer.anchorPoint +

[box.left*textLayer.scale[0] / 100,

box.top * textLayer.scale[1] / 100] +

[box.width * textLayer.scale[0] / 100,
box.height*textLayer.scale[1] / 100] / 2;

How to make a box round?
Open Roundness property of the shape box and increase the value.
How to change padding?
Change horizontalPadding and verticalPadding in the first expression.