Splitscreen
If you would like to do this live, go here: Live "Split-Screen"
Adobe Premiere/After Effects
Step 1. Superimpose one clip over the other. Add one clip to the Video 1 track, and add another clip to a video track with a higher number. Video tracks numbered 2 or higher are also called superimpose tracks. In this example, you'll be working with the clips on the Video 1 and Video 2 tracks. Video tracks 4 and 5 (the jacks) will also be visible, but you won't be making any changes to them.
Note that the Video 1A and 1B tracks, if displayed, are for editing only. Any clips you want to superimpose must be on a superimpose track.
Step 2. Preview the clips. Scrub (drag through the Timeline ruler) while pressing the Alt key (Windows) or the Option key (Mac OS). Holding down the Alt/Option key previews any applied transparency or effects as you scrub.
Notice how tracks below Video track 2 (the background) don't appear in the Program view on the right side of the Monitor window. This is because track 2 has no transparency. The backgrounds of the clips in tracks 4 and 5 are already keyed out (have transparency applied to them), so we can see through them to the tracks below.
Tip: If you want to preview the Video 1 track, you can click the eye icon in the Video 2 track to hide it. Just remember to make the Video 2 track visible again before continuing.
Step 3. Apply transparency to the superimposed clip. Select the clip in Video track 2 in the Timeline and choose Clip > Video > Transparency. Position the pointer on the bottom left corner point in the Sample area. When the pointer icon changes to a finger icon, drag the point halfway up the left edge of the frame. The white area you see will be transparent when you preview.
Tip: The Video menu is also available from a context menu. Right-click (Windows) or Control-click (Mac OS) the clip in the Timeline to see this menu.
Step 4. Finish adjusting the superimposed layer. Drag the bottom right point in the Sample area about halfway up the right edge of the frame. Now the entire bottom half is hidden, making it possible for clips on lower tracks to show through.
Ulead Mediastudio
You'll need to go into Editor, and open the project properties. change the frame size to whatever is double the width (or double the length, if you're stacking them) of the clips (so if both your clips are 320/240, make the frame size 640/240 or 320/480, etc).
Lay the first clip in the first Video track, amd the second clip in a track underneath it. Start with whichever one will be on the left. Right click the clip, select Moving Path, and drag and drop one from the production library that comes up (preferable a simple one, where the video doesn't zoom - I use the one the scrolls left to right). You'll then have to change to coordinates so the video stays static. change the frame size to the original clip size (since Editor will automatically resize it to the project frame size). Then make the X/Y coordinates the same for both starting and endpoint - which keeps the clip from moving (the X will need to be half the width, the Y will be half the height - X:160, Y:120 for a 320/240 clip).
For the clip that will be on the right, you'll do the same thing, except for the X/Y coordinates. The Y should be the same as the first, but the X should be half the width (of your original clip) LESS than the total width of the PROJECT frame size (did that make sense? - if not, you can just eyeball it with the outline in the left field)).
The second clip needs to be in one of the overlay tracks (V1, V2, etc), not either of the two primary tracks (I tried it with clips in VA and VB and only the one in VB showed up, leaving the left half black).
