how to do simple recording of web audio

The easiest way is to run an application that can capture the audio stream and let it write to a file. Then import this file to Garageband.

I am using Audio Hijack - it is very easy to use (https://www.rogueamoeba.com/audiohijack/), but there are other applications, that can record streaming audio to a file, see:

http://www.iskysoft.com/audio-recorder-mac/top-audio-recorder.html

coolpontiac wrote:

thanks but are you sure there is no way to do a simple recording of the mac's own audio output without having to get a 3rd party tool?

it seems hard to believe that a platform as mature as mac os (e.g. its garageband app) cant simply take as input the very audio that is flowing from its output (ie whatever h/w,s/w that is driving the internal speakers).

There may be, but I don't know of any native Apple application that can do that. I think, it is intentional. If you can simply capture the native audio output stream from a webpage or a video you are playing, you could capture copyright protected material.