All you wanted to know about Soundflower
iShowU HD (v1 also) use a third party driver called Soundflower to hook into the Audio.
We'd love it if Apple had made it so that we (as developers) can record audio from an application, or from the computer itself but unfortunately and for whatever reason there is no API to do this.
You can think of Soundflower as a pipe. Whatever goes in one end comes out the other. In this case we're talking about audio. Whatever audio is played to the Soundflower 2ch output appears on the Soundflower 2ch input.
So to record audio, iShowU does the following:
- It looks to see what you have the Sound Output set to, and remembers this.
- It changes the Default Sound Output to the Soundflower 2ch device. You can see this if after starting iShowU and enabling "record computer audio" you then examine the Output tab in the Sound preferences.
- iShowU itself plays the audio it's hearing on the Soundflower 2ch device to the device that it saw in Step (1) above, otherwise you'd not be able to hear anything.
- Finally, iShowU records the sound coming from the Soundflower 2ch device.
How can I tell if I have Soundflower installed?
If you go into your System Preferences under Sound, it should be present in your Input as well as your Output tabs.
I can't install Soundflower from the application.
You can go to this site for an overview of Soundflower or directly download the driver here.