Using the playhead for control

- So far, we have seen many expressions…that control different properties.…Now, let's get to where the time position…of the playhead can determine the value…that the property will have throughout the expression.…But not just the timing of the playhead…can determine values.…Any other property can.…Let's go ahead and open composition 4.1,…use the playhead for control.…In here, you're going to see a single sprocket.…If you play it, there's nothing really changing in here.…

Let's go ahead and add an expression…to the opacity of this sprocket.…So select it, press the letter T, and add the expression.…Now, what we're going to do is we're going to make use…of the expression language menu.…Go ahead and click on this little play button here,…and go under interpolation,…and choose Linear, T minimum, maximum,…value1, value2,…and it writes the expression for you.…

Well, it's actually writing…what the expression is referring to.…If we were to commit to this we would get an error,…because we actually have to replace these by real values.…