Audio Plumbing

picture-1.pngI’ve been trying to make a screencast of Skype conversation. And I thought it would be pretty simple. But as so often happens, there are technical issues to overcome that can make things so much trickier than you first thought they would be.

I’ve done quite a bit of screen capturing before, usually for short training videos on how to do certain software tasks. In fact I made a CD for a commercial training organisation a few years back that had over 80 tutorial screencasts on it made with Capture Cam Pro, so I figured I knew how to do this stuff. I’ve also been using Jing lately to make short screencasts on tech tips for our school network users. I think that screencasting is a great way to learn (and teach) this sort of practical, “show me” sort of stuff. Atomic Learning is another excellent resource based on this idea.

So I wanted to make a couple of screencasts to demonstrate how to use the features of Skype. I’d been using Snapz Pro X on the Mac, but wasn’t totally happy with it. I’d heard good things about iShowU so I downloaded a copy to try. I only had to use it a couple of times before I realised that it was going to be well worth the $20 they were asking for it, so bought a copy immediately. Easy to use, lots of professional options, and very customisable. A cool tool.

So I set up a screen capture, fired up Skype and called the Skype call testing service at echo123. iShowU captured all the on-screen action easily, as well as my microphone input, BUT not the audio coming out of Skype. Hmmm, that’s no good… I can’t do a demo of Skype if I can’t hear the conversation played back in the screen capture. I thought of a bunch of ideas to solve this, including using Audio Hijack Pro to capture the Skype audio, iShowU to capture everything else, and then dropping it into iMovie to edit them into a single movie but that seemed like it was all getting too hard and time consuming. I’m basically quite lazy, so I wanted a better, more elegant solution.

After quite a bit of trial and error I finally figured out how to do this, so here is my solution in case you ever need to do it yourself.

picture-2.pngThe trick is to use Soundflower, a Mac system extension that lets you route audio around the system in non-standard ways. From the Soundflower website, it says “Soundflower is a Mac OS X system extension that allows applications to pass audio to other applications. Soundflower is easy to use, it simply presents itself as an audio device, allowing any audio application to send and receive audio with no other support needed. Soundflower is free, open-source, and runs on Mac Intel and PPC computers.”

So, here’s how you do it – or at least it’s what eventually worked for me after much trial and error…

  1. First, I set the audio inputs of the Mac to Soundflower (2ch), that’s input, output and system.
  2. Then in the Skype preferences, set the Audio input to your desired microphone (I used a USB headset mic) and the Audio output to Soundflower (2ch). I set the ringing to Soundflower as well, but that’s probably not so important.
  3. picture-3.pngFinally, in iShowU, set the Input selection to Record Microphone Audio, Force it to Mono, and turn on Record System Audio. Set the microphone input to the USB headset (in my case). I also prefer to get the monitor feed while both previewing and recording, so turn that on if you want.
  4. By the way, setting the compression to H.264 makes a huge difference to the size of the final files.

There you have it. From what I can figure out, it works by routing the Skype microphone input to Soundflower, then routing its output to be the Mac’s regular audio input as a Soundflower stream. Then the Mac uses that diverted audio stream and treats it as the regular mic input to the computer (except after passing it via Skype it now has the entire Skype conversation in it) and then using iShowU to monitor the standard audio feed, which now contains the Skype audio. This may all be totally useless information to most of you, but for someone out there it may just save you a whole lot of time. I hope so.

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CC BY-SA 4.0 Audio Plumbing by Chris Betcher is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

3 Replies to “Audio Plumbing”

  1. whoooosh! over my head. this from the girl who can’t get her mic working. so, uh, don’t take it personally! i’m working on my mic right now.

  2. I use iShow you as well and really like it. I have played with the audio settings and Soundflower but found this a really useful explanation. Maybe you could put in on my wiki so as to make this info an ongoing resource

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