Cropping out split-screen
After Effects | Sony vegas | Adobe Premiere
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Source Video
Open After Effects
First you will need to create a new composition,So open After effects,Create a New Project. And make new new composition

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These settings should be ideal for machinima video; adjust the Duration option to give yourself enough time on the timeline for your video.

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Import your file(s)

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Drag the video(s) onto the timeline
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Expand the transform options. Right click Positon>Edit Value
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Enter these numbers

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Right click your clip and Create a mask

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Expand the mask options(1) and click Expansion. Then Adjust the Mask Points(2) move the bottom 2 points to cover the bottom of the screen.

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Now to export your clip. Click Composition>Add to render Queue

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Adjust your settings by clicking the blue text,and set the output directory to Desktop or whatever folder you want. Then Click the Render button.

Final Outcome