I am often asked about details related to recording screencasts, so here goes.
I use Snapz Pro X to record the movies. It’s a little pricey ($69) but I have tried several of the alternatives, and none of them gave me a result as good as Snapz Pro X.
If you do a lot of key presses in your screencast then you may find KeyCastr useful. It is an Apple-style keystroke visualizer.
For the audio I am using a Logitech (USB) desktop microphone. It works great, but I would prefer a headset since I occasionally move around while recording and this can change the volume of my voice. If anyone has headset recommendations, please add them to the comments.
One thing to check is the Input Volume for your device in System Preferences → Sound. I found that if I have Auto mic input gain enabled in Snapz Pro X (the default) then it will set my Input Volume to 50% when I start recording. So definitely check if this setting has the same effect on your system!
I have created a user account specifically for recording screencasts. The resolution for this is 800×600 so that I can record the full screen and get a decently sized movie without panning around or having to scale the result (and get a blurry movie).
Normally I first go through the stuff I want to show without recording it, just talking to myself. This gives me a feel for where trouble will arise and which things I need to prepare better or be sure to have memorized.
It isn’t easy to do them as one-take though, and sometimes I have to start over or cut them short — if I did more of them, I’d invest the time to learn a video editing program so that I could edit the videos after having recorded them, perhaps even record the soundtrack after having recorded the actual video and also skip boring parts in editing.
But for now, I think the time it takes me to get them right as a one-take is still shorter than having to stitch together multiple recordings and/or add a soundtrack in editing.
When done recording I save the file with the Animation codec, millions of colors, and highest quality. Basically I want loss-less, but I think this option is what gets the closest. Be sure to also enable audio when saving.
I use QuickTime Pro ($29.99 from the Apple store) to export it using the H.264 codec, frame rate set to 10 and quality set to high.
For the audio part I use 64 kbps AAC. The audio part of your recording is actually larger than one would think (a 10 minute movie with 128 kbps audio uses 9 MB for the soundtrack alone) so be sure to use compression here.
A last option is the Prepare for Internet Streaming which you should set to Fast Start — this is what allows the movie to start playing before it has been fully downloaded.