user1434: It's fairly common to see videos in which, to accompany a piece of music created using overdubs, we see a split screen showing the artist performing each overdub.
What functions, in which software, may be used to create videos like this?
Is it a matter of mixing the audio separately, then manually synchronising the video, or is there software that automates the process?
Answers for any software are welcome, but budget answers (iMovie, Movie Maker) are welcome, as well as any software designed for this specialised purpose.

user1802: Split screen is an effect, that most video-editing softwares offer. In some programs you need to scale, crop and position the snippets.
Usualy you have ONE audio track. Most video editing programs allow to do basic sound editing, but that is not a "professional" workflow. Simple reason: most video editing tools use 1 frame a smallest unit on the timeline. Which makes it difficult to exactly synch audio-tracks.
Synching the video is easier, when you use a clapboard when recording the video. that way you have a "mark" on the video and audio track, that is pretty easy to find. (That's what this thing was and is used for).
Software, that could do the trick: Avid Free DV, Wax and iMovie should help you. (easy video tutorials on youtube - search for "splitscreen imovie")

user636: WAX is an freeware video editing program. 
You can create a split screen effect with either a source image or AVI video file. Import then source files into the MediaPool (Project -> Insert Tracks) then position them on seperete layers on the timeline.
From the MediaPool change to the Plugin Presets tab and drag the desired split screen effects over the video/image you wish to apply.
[Full Size]
 
[Full Size]

I've shown an example above, in the second screenshot you can see I played with some of the settings to adjust the width of the split screen. You can also change the size and position of the video. 

user2287: In general you should be able to do that with any video editing software.

Professionals use timecode-synced equipment for this job. Low budget productions do this with simple audio marks at the beginning and the end of a take. You can do this simply by clapping with your hands. But using a slate gives you a more significant mark (peak).
The main audiotrack is a separate mix. This is the reference. The videos will be synced track-by-track to this reference. Usually this will be done manually. But Final Cut Pro X can also do this automatically with great success. 
The splitscreen itself is nothing special. Just adjust size, crop and position of a track or clip as you like. 


1434: <p>It's fairly common to see videos in which, to accompany a piece of music created using overdubs, we see a split screen showing the artist performing each overdub.</p>

<p>What functions, in which software, may be used to create videos like this?</p>

<p>Is it a matter of mixing the audio separately, then manually synchronising the video, or is there software that automates the process?</p>

<p>Answers for any software are welcome, but budget answers (iMovie, Movie Maker) are welcome, as well as any software designed for this specialised purpose.</p>
 1802: <p>Split screen is an effect, that most video-editing softwares offer. In some programs you need to scale, crop and position the snippets.</p>

<p>Usualy you have ONE audio track. Most video editing programs allow to do basic sound editing, but that is not a "professional" workflow. Simple reason: most video editing tools use 1 frame a smallest unit on the timeline. Which makes it difficult to exactly synch audio-tracks.</p>

<p>Synching the video is easier, when you use a clapboard when recording the video. that way you have a "mark" on the video and audio track, that is pretty easy to find. (That's what this thing was and is used for).</p>

<p>Software, that could do the trick: Avid Free DV, Wax and iMovie should help you. (easy video tutorials on youtube - search for "splitscreen imovie")</p>
 636: <p><a href="http://www.debugmode.com/wax/" rel="nofollow noreferrer">WAX</a> is an freeware video editing program. </p>

<p>You can create a split screen effect with either a source image or AVI video file. Import then source files into the MediaPool (Project -> Insert Tracks) then position them on seperete layers on the timeline.</p>

<p>From the MediaPool change to the Plugin Presets tab and drag the desired split screen effects over the video/image you wish to apply.</p>

<p><em><a href="https://i.stack.imgur.com/gGRd4.png" rel="nofollow noreferrer">[Full Size]</a></em></p>

<p><img src="https://i.stack.imgur.com/gGRd4.png" alt="enter image description here"> </p>

<p><em><a href="https://i.stack.imgur.com/WMycR.png" rel="nofollow noreferrer">[Full Size]</a></em></p>

<p><img src="https://i.stack.imgur.com/WMycR.png" alt="enter image description here"></p>

<p>I've shown an example above, in the second screenshot you can see I played with some of the settings to adjust the width of the split screen. You can also change the size and position of the video. </p>
 2287: <p>In general you should be able to do that with any video editing software.</p>

<ul>
<li><p>Professionals use timecode-synced equipment for this job. Low budget productions do this with simple audio marks at the beginning and the end of a take. You can do this simply by clapping with your hands. But using a slate gives you a more significant mark (peak).</p></li>
<li><p>The main audiotrack is a separate mix. This is the reference. The videos will be synced track-by-track to this reference. Usually this will be done manually. But <strong>Final Cut Pro X</strong> can also do this automatically with great success. </p></li>
<li><p>The splitscreen itself is nothing special. Just adjust size, crop and position of a track or clip as you like. </p></li>
</ul>
