Cropping out split-screen
After Effects | Sony vegas | Adobe Premiere
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Source Video
Open Premiere ,Drag your clip onto the timeline(1) Now click over to the effects controls window(2) Expand the motion options and Change the Position to the value showen "320 360"

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Now expand the Transform subfolder in the effects window. And drag "Clip" onto your video on the timeline.

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Expand the clip options in the effect controls window. Adjust "bottom" as needed(1), usually 50.
Final Outcome