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If you have the Exercise Files that come with this lesson, go ahead and open up the comp 01_Layer_Practice*starter. If you don't have the Exercise Files, just import any few sources in After Effects, create a new comp, drag your sources into the comp, and you can play along. We're going to start gently with the simple concept of how the horizontal and vertical arrangement of layers in the Timeline panel affect what you see in the Comp panel. Now as you probably know, the Comp panel displays your current composite of layers underneath the Current Time Indicator.
So as you drag your Current Time Indicator through a project, you get an idea of how things change over time. I am going to move the Current Time Indicator to where two layers overlap in the Timeline. The stacking order in the Timeline affects which layer takes precedence when it's rendered to the Comp panel. Mainly the layer on top typically wins. If I was to take that layer on top and drag it underneath the other layer, you'll notice this black line indicates where I am about to drop this new layer. Now the new layer on top takes precedence and is what is drawn inside the Comp panel, simple enough.
Of course, there are exceptions to every rule. One exception is if you have the 3D Layer switch enabled for layers. In that case, the distances of layers from the virtual camera will also have a big impact on how things are rendered inside the Comp panel. Secondly, anything that affects the alpha channel for layer, such as Opacity if I press T to reveal it, also affects what you see in the Comp panel. There is Opacity. There is ways of modifying the alpha channel such as masking. There is also the subject of blending modes, which we'll be getting into later in this lesson.
But in general, it's the stacking order that determines who gets precedence at a given point in time. Now let's talk about sliding these layers bars in time and to make it more clear what we are doing, I am going to go down to the lower left corner of the Timeline panel and open up this Expand or Collapse In/Out/Duration/Stretch Panes button. I click on that, and now I get a lot more information for my layers. Where they start in the composition, where they stop, the duration, and when that they've been time stretched. We are not going to cover time stretching in detail in this lesson.
So if you have a limited amount of space in your monitor, you can right-click on any column header, and select Hide This to make it go away, and buy yourself back some more space. But since I have a pretty wide monitor, I am going to leave this open for now. And I am going to press T just to hide Opacity and clean things up. Individual layers in After Effects have two sets of In and Out points. One is the external In and Out, where do they start and stop in relation to an overall composition or Timeline.
You can jump to those external points by pressing I for In, then I'll move the Current Time Indicator to the In point in the Timeline for the currently selected layer, and press O to jump to the Out point, the external Out point in the overall composition. You'll notice with the layer bar that you see the strongly colored area, but you also see these ghosted areas before and after in the case of this layer. These ghosted areas indicate that there is additional source material in this layer that we are currently not seeing in this composition.
This is where other set of In and Out points come to play. The Internal In and Out points for a layer. Of all source material you have in in a footage item, what is the In and Out for that source that you chosen to display in a composition. That is related to, but different than the external In and Out, what frame of that layer do you see at a given time in the overall composition. If you're using an entire source, you will not see these ghosted areas. If the internal In and Out trim points equal the start or end of the source itself, you'll see this little black corner up in the edge of the layer.
That indicates you are right up against the start of layer or right up against the end of the layer. Moving a layer in the Timeline is very easy, and as I do so, watch how the In, Out, and Duration values change in these columns. As I drag a layer earlier or later in time, you're seeing it's external in and out times. Where does it start and stop in relation to your overall composition. Notice that I was not moving the Current Time Indicator, but the image in the Comp panel was updating as I slide this layer relative to the overall composition.
If you have a particular time that you'd like a layer to start, you can move the Current Time Indicator to that time, or click on the Current Time for the Timeline and enter something like 5 seconds and 15 frames. Press Enter and then with a layer selected, press the left square bracket to force it to start at that time or the right square bracket to force it to end at that time. This again slides the entire layer relative to the composition. It does not change what portion of the source material you are using.
It just changes the external timing relative to your whole Timeline in a comp. In the next few movies, we'll get into changing what portion of the source material you are using in this composition. How do you trim the internal In and Out points.
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