CamTwist is very clever free software for the Mac that lets you switch between different video sources on your computer, including webcams, movie files and also your computer’s desktop. You can add a range of video effects, titles and other useful overlays, in multiple layers – such as news tickers (powered by RSS), logos and graphics, and then output the result as… another video source on your computer.
What this means is that you can use this program to intercept the video going into other programs that lets you choose a video source – think video editing programs, video chat programs (eg Skype) and flash-based online video services such as Ustream, JustinTV, Stickam and WorldTV.
Another way of looking at it is that the program lets you create your own software-based live video mixing studio that sits well with almost all other video programs, including streaming web video services.
You can take the video from your webcam, pimp it up broadcast style, and then send it onwards to a video chat session, recording or online video streaming session. Amaze your friends in Skype, do highly professional stuff online – possibly you’ll do both.
The intercept approach is genius because of its flexibility, and it explains why leading web broadcasters like Chris Pirillo and Rhett & Link are using the software, made by an enthusiast, and supported through generosity of donations.
CamTwist is highly powerful (see demo video below), and you only have to see the results of that on the two sites I’ve just mentioned – both Chris Pirillo and Rhett & Link use the software for all of their live video mixing and compositing.

While CamTwist excels is in its depth and flexibility, it suffers a little in ease-of-use at this time. This should not put you off as it is well worth the investment, and the interface will improve as the software develops. It’s still early days.
You can learn the interface in about 30 mins and once you’ve got the hang of it you’ll quickly come to appreciate the power that it provides you, and most probably love the developer who made it. In short it is highly empowering software that has nothing else like it.
If you want a little more convincing before making the leap, I highly recommend reading Michael Pick’s excellent coverage of the software.

Introductory Guide to CamTwist

There are two distinct parts to the application – the older legacy part of the application – the main window, which lets you set up sources and effects, which effectively become buttons for the main Studio window where you do the live switching. Basically you do all your experimenting and configuring in the first window, and the live switching in the second.
I recommend reading and watching the two Quick Start video guides on the site wiki – the first is for the main (legacy) window of the application, and the second is for the new Studio window. It’s important to understand that the main, older window represents where the project is coming from, and the Studio window where it is going. Any quirks of use can be understood much better if you keep this in mind.
Another important point is that the program does not control or switch audio. The audio circuits of a Mac are separate from the video and this can actually provide you with much greater control. It’s not yet been a problem for me, but I may revisit this subject later if it becomes so.
For an alternative viewpoint of how it can be used, Chris Pirillo’s fascinating explanation of how he produces his online TV show is well worth a look.
This article is a stub – I intend to add to it over time.