Creating masking tracks in Vegas

by Gary Rebholz

Vegas software has always offered robust video compositing features which make it possible to create sophisticated composited sequences without opening a dedicated compositing application. When the Vegas team expanded the concept of parent/child track relationships a couple of versions ago, the process also expanded the possible ways in which you can use compositing to create masking tracks. In this article I'll take a look at creating mask tracks in Vegas software so that you can begin to get a handle on the possibilities that these techniques bring to your video editing projects.

Let's start with a simple technique and get more sophisticated from there. First though, what do we mean when we say we're going to create a masking track? Basically, you can use the content of one track to show only specific portions of the content of a track below it on the Vegas timeline. In other words, you can use track one to mask out portions of track two while letting other portions show through.

Think of two pieces of paper, one stacked on top of the other. Let's say the sheet on the bottom has a picture on it and the one on the top has a word printed on it. If you take a pair of scissors and cut the word out of the top sheet, you'll be able to see through to the bottom sheet and thus see the portion of the picture that shows through the word making it look as though the word was filled with the picture from the bottom sheet. We can do this same thing in Vegas software.

Start with a project that has a video event on track two and a text event on track one. Make sure the text event has white text on an opaque black background. Tracks in Vegas software act much like the stack of papers we discussed a moment ago. Specifically, when you stack events on separate tracks one above the other, in the Video Preview window you see only the contents of the event on the top track assuming the top track is completely opaque. So, at the moment you only see the text and cannot see the video on track two.

When you create a masking track—also known as a mask roll—in Vegas software, you essentially tell the software to treat anything in the track that's white as if it were transparent. To create the masking relationship, click the Compositing Mode button in the track header for track one. A long list of compositing modes appears and you can experiment with the various modes later. For now, choose Multiply (Mask) from the list as I am in Figure 1. In the Video Preview window, you can see that the video from track two now shows through the text in track one as shown in Figure 2.

Figure 1

Figure 1: Vegas software has a number of compositing modes that control the way the software blends clips on one track with the clips on a track below it in the timeline. To create a mask, you'll set the top track's compositing mode to Multiply (Mask).


Figure 2

Figure 2: Now that you've transformed track one into a mask roll, Vegas software treats the white words as transparent and you can see through to the footage on track two.

Now, in reality, you didn't really need to create a masking track to achieve this effect. You can get the same results if you use transparent text instead of white. But you might not always want to use text on the mask track. Perhaps you want to use a geometric shape or some other artwork for the mask. For that matter, maybe you want to use another video on the mask track. Then things really get interesting.

Although here we used a simple black and white image, you could use an image with shades of gray or even a full-color image. When you do, Vegas software creates a level of transparency that corresponds to the level of white in any portion of the media. Take, for example, the case of a simple gradient from white on one side to black on the other. Replace the text on track one with the Linear White to Black preset of the Color Gradient media generator. This creates an effect where the video on track two becomes more visible as the level of white on track one increases as shown in Figure 3.

Figure 3

Figure 3: Here I've replaced the text with a white-to-black gradient. In the Video Preview window you can see that the mask lets more of the media from track two show through as the level of white increases toward the left side.

Now take it a step further. Things really get interesting when you use a full-color video file on the masking track. Try it and see what results you get. Imagine how you might make use of that as a special effect in your videos.

Now, imagine the effects you could create if you start using the keyframe controller to change things over time. For instance, you could create keyframes in the color gradient's keyframe controller area that makes the gradient grow through stages over time from fully black to a black-to-white gradient and then to fully white. This creates the effect of gradually sliding off a black veil with blended edges that obscures the video from the lower track. The more creative you get with your keyframing and masks, the more interesting effects you'll be able to create.

For the sake of this discussion, let's go back to the white text on black background on track one. Put another video event on a new track directly below the two existing events. Use a clip that looks strikingly different from the clip you used on track two. As you might have expected, you can't see the clip on the third track in the Video Preview window, but we can get a bit more sophisticated in our masking to solve that problem.

Our challenge now is to have the text filled with the video clip on track two over the top of the video from the clip on track three. We'll use the parent/child relationship between tracks to accomplish this.

Click the Make Compositing Child button on the track two track header. You don't see any difference in the Video Preview window, but notice that the track header for track two sits indented and embedded within the track header for track one. This indicates that a parent/child relationship exists between these two tracks and you can use track one to control the behavior of its child, track two, in several ways.

We can use one of those ways to complete the masking mission. Click the Video FX tab to bring the Video FX window to the front of the window docking area. From the list of filters and effects on the left, choose the Mask Generator filter. Drop the Luminance Mask preset onto the track one track header. When you use luminance to create the mask, that luminance, or the brightness of the track, determines the transparency.

Note that you could also drop it onto an individual event, but applying it to the track header ensures that the filter has an effect on every event in the track. Finally, to make the words stand out a little better, click the Parent Motion button on the track one track header. In the Parent Track Motion dialog's keyframe controller area, select the 2D Shadow checkbox. This adds a shadow to the composited tracks.

You've achieved the desired effect as shown in Figure 4. You can see the words from track one, filled with the video from track two, floating above the video on track three.

Figure 4

Figure 4: With track two designated as a compositing child of track 1 and a Mask Generator filter applied to track 1, you've created a mask that fills the words on track one with the video on track two over the top of the video on track 3.

And now that you understand these powerful techniques that you can use to create masking tracks, experiment with them in your video projects and see what interesting and innovative effects you can come up with!

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