Need: Mac equivalent of audio input of windows "stereo mix"

Soundflower (free) will let you patch system audio into a recording app.

You could also consider using Wiretap or one of the Audio Hijack programs (both commercial), these have built-in recording.

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Here's how to record your Mac's audio for free. Lotsa steps, but remember that some of this stuff is one time only

1. Download Soundflower. Drag the Soundflowerbed app into your Applications folder, then run the installer that's also in the disk image (do it in that order because the installer will require a reboot, and otherwise you'd have to open up the disk image a second time just to grab Soundflowerbed).

2. Grab a copy of Audacity, if you don't already have a recording app you like.

3. Launch Soundflowerbed, so that it's in your menu bar. You can always add it to your login items if you use it regularly.

4. Launch Audio MIDI Setup, in your Application/Utilities folder. Under the Audio Devices tab, set the default output to Soundflower (2ch).

5. Go up to the Soundflowerapp menu and tick "Built-in Audio" (or whatever you normally use) under the 2ch section. Toggle this between that and None, while any old app that makes sound is running, to verify that audio is being sent there (because the output cuts in and out).

6. Launch Audacity. In its preferences, under the Audio I/O tab, set the playback device to built-in audio and the recording device to Soundflower (2ch).

7. You're ready to record. Audacity will turn off Soundflower monitoring as soon as you hit the record button, and instead send its own monitoring out to the speakers (but since Soundflower is its input, it's all the same stream to your ears). After you're done recording, you can re-enable direct Soundflower monitoring again from its menu.

All that's easier done than said, it's really just a few clicks if you take the explanation out of the way.

8. When you're done capturing, you can put things back to normal back in Audio MIDI Setup.

[edit: adding for convenience: Over in Audio MIDI setup, one of the things you can do is set Soundflower to be both the default input and output, then Soundflowerbed will let you monitor through the real speakers. ]

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You can of course substitute some other audio app, this one is a good illustration, though. I'm not really sure what's up with recording a video stream and trying to grab audio separately, maybe you could mention what apps you are trying to use here?

Ok, I'd still try Soundflower first, before cable loops. Over in Audio MIDI setup, one of the things you can do is set Soundflower to be both the default input and output, then Soundflowerbed will let you monitor through the real speakers. By going through Core Audio that way, assuming that Parallels and the apps you are running will cooperate, you can avoid the line noise and resampling hassles from the cable loop.