Here’s my test of audio/video screen capture using ScreenFlow, in which I use Google to find Waldo. It was recorded on a Mac OS X 10.5 machine with a Logitech Desktop Microphone.
The final Quicktime video is 960×600 pixels (about 50% of the original screen size) It is 1.04 minutes long, and 7.7 MB in size. I used the “Web – High” setting (H.264 video encoding at 850 kbits/sec. AAC sterio audio at 96 kbits/sec). The original video was full-screen; I didn’t attempt to do a full-size export.
Observations: ScreenFlow offers a lot more options than Silverback. For example, when doing the capture I could choose which of my Mac’s iSight cameras I wanted to use (the MacBook Pro’s built in iSight or the one on my external monitor) as well as which monitor to use (the MacBook’s or the external one). It includes 11 export options, and a number of video tweaking options within the program, including the ability to move/resize the picture-in-picture video and the ability to add on-screen text. I like Silverback for its fire-and-forget nature, but I think ScreenFlow offers us more long-term flexibility.