A Skype-Like App with Open Source Roots

January 3rd, 2006

Anybody who has dabbled with CoreAudio programming on the Mac is probably familiar with the indispensable MTCoreAudio framework, by Michael Thornburgh. The framework makes it easy for Cocoa programmers to harness the power of CoreAudio’s HAL (Hardware Abstraction Layer) by wrapping some of the major components in Objective-C wrapper objects.

What has Thornburgh been up to lately? MTCoreAudio releases haven’t come as fast and furious as they did in the early days, so he must be keeping busy. It turns out he co-founded a company called amicima (pronounced like Italian – think “da Vinci”), whose mission it is to develop robust p2p infrastructure protocols for a variety of possible uses. Blah blah blah, right? Hasn’t everybody developed a p2p protocol suite? What’s left to develop? I thought so, too, but amicima’s technology offers some compelling features.

The company has just released a Mac OS X version of their flagship technology demo: amiciPhone. This program doesn’t make a great visual splash – it’s not going to win any beauty awards. It’s a “technology demo” in the best and worst senses of phrase, highlighting a robust infrastructure with minimal attention to the application’s user interface. Still, Thornburgh’s solid Cocoa-based interface provides access to the voice, file transfer, and text chat features of the program. And while he’s no visual designer, he couldn’t resist the temptation to add some Mac-only niceties. He sent me a PDF file through the program and, before agreeing to accept it, I was treated to a graphical preview of the document’s first page. That’s cool! amiciPhone is “a lot like Skype” when judged purely by its feature set. But the application isn’t out to dethrone the existing VOIP giants – it’s merely a demo of what the company’s underlying technologies might be used for. (Not that somebody else couldn’t use the technology to write a Skype-dethroner!)

Some things I noticed during my long-distance chat/demo with Thornburgh:

  • Voice connection survives change of IP address. This is pretty amazing. Thornburgh opened up a voice chat with me on his PowerBook. He then proceeded to pull the plug on the ethernet, causing a few seconds timeout while his computer came to terms with the backup Airport connection. When his connection came back online, he was chatting away again. He plugged his computer back into ethernet and, because of the Mac’s much quicker switch to the hardwired connection, his IP address (confirmed with tcpdump) switched seamlessly without any interruption in voice quality.
  • Slick congestion control. I’ll have to take Thornburgh’s word for it, but apparently most VOIP programs suck when it comes to managing voice and file transfer at the same time. I don’t have anything to compare with (unless you count the numerous times I’ve failed altogether when trying to transfer a file with iChat), but I was impressed when Thornburgh’s voice continued uninterrupted while a giant QuickTime movie started transferring from his house in California to mine in Massachusetts.
  • High audio quality. This is a testament to CoreAudio, MTCoreAudio, and speex, the open source audio codec they’re using for the demo. I launched amiciPhone on my Mac with a MOTU 828 audio interface attached, and within seconds I was hearing Thornburgh’s voice through the speakers on either side of my office. The demo allows essentially any CoreAudio output or input device to be selected, so you can use a specific device for amiciPhone without changing your default sound settings.

The fact that this was all happening over a secure AES-128 connection with open source components got me wondering if it wouldn’t be too difficult for an application like Adium to incorporate parts of it, maybe facilitating a “voice chat” add-on separate from whatever protocol is being used for the text-chat functionality. I don’t know if the Adium team already has a plan to support voice, but since Thornburgh’s company is licensing the technology in both GPL and commercial forms, it could be an appealing option for both open source and well-funded software teams.

Of possible interest to Cocoa developers is something called MObj, which betrays Thornburgh’s passion for Objective-C style dynamic programming. This component of the amicima suite is licensed under a generous BSD license, and promises a number of Foundation’s core features in a cross-platform, ANSI-C format. I’ll have to keep that in mind next time I’m forced to write code away from the comforts of Cocoa.

I’m looking forward to seeing what technologies amicima comes up with in the future, and more importantly what creative developers out there might end up doing with them. In the mean time, maybe some kind soul will donate a UI overhaul to amiciPhone – or at least an icon!

One Response to “A Skype-Like App with Open Source Roots”

  1. Dana Leighton Says:

    Hi,

    I submitted a product enhancement ticket to the Adium team regarding this – I think it’s a good idea.

    Cheers,
    Dana.

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