Track Mattes – Step by Step
Picture this, a static shot of a series of buildings, one of the buildings has a large advertisement board attached to it and you want to use this clip but replace the advertisement board with a simulated video screen which shows a video of your choice.
On Track 1 place the shot of the buildings, adjust it to the desired duration
Make sure the timeline cursor is in a position that make the clip visible in the monitor window
Then create a new title, and in the title window create a white box that just covers advertisement board.
Place the title on track 3 and adjust the duration to the track 1 shot.
On Track 2 place the clip you want to appear on the advertisement board and adjust its duration to suit.
In the Effects tab type track matte in the search box and the preset will be shown
Click on it and drag it onto the clip on Track 2
Click on the clip on track 2 to highlight it and in the Effect Controls tab you will see the Track Matte Key effect, open up the effect by clicking on the arrow so you see the text Matte:
From the drop down menu select Video 3
Job done, you have the effect showing
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If you cannot achieve what you want with the Titler, you will need to use Photoshop.
Export a still frame from the clip you want to use, make sure it is the same pixel x pixel resolution as the video clip
Open the still in Photoshop and then create a new blank layer above the image, select it and fill this black and turn the opacity down so that the still is visible
In the Layers window create a new Layer Mask
Create a box using the Marque tool approximately covering the space you want to remove from the video clip and with the marching ants visible
Use the Edit > Transform Path > Distort option to have control points visible on the box
Move them around until they cover what you want on the video clip still press Enter and press Ctrl and X to remove the selected portion
Click on the still in the layers window to select it and drag it to the trash can
You should now have a single black box with a grey and white checker board effect behind it, this is the alpha channel that Premiere will need but before you save it put the opacity slider back to where t was
Save the file but make sure the Alpha Channel box is ticked
Import this into Premiere and use it in lieu of the title mask I explained earlier
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I’m not finished yet
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If your scene has camera motion the effect is still possible but you need to use After Effects and for this there is a video on the Creative Cow website that shows how to do it.
http://library.creativecow.net/devis_an ... acking-1/1