As I travel I often fill my down time listing to various podcasts. The IT Conversations series have been a great source of inspiration and education. Today they posted a podcast of Jonathan Christensen, General Manager, Audio & Video at Skype. He was speaking at the 2009 Emerging Communications Conference on March 3, 2009. In his keynote presentation, called Codec Evolution and Industry Proposal, he announced their new, in-house developed SILK codec and the fact that it was being licensed to third parties for free.
This is definitely worth a listen, and good study for me as I set about preparing for my Astricon 2009 presentation about HDVoice.
There has been for many years a subtle conflict ongoing in telecom space. Various vendors have created digital encoding techniques (codecs) that target common network issues. Since various network realities exist so too do various approaches to the problems faced. So a range of codecs exist in the marketplace. Typically a high-quality solution comes with an associated cost, reflecting the very fact that the solution has merit.
The poster-child for this is the G.729a codec. Over time this patented codec has become the industry standard low-bitrate codec for voice applications. Who can argue. It works well. It squeezes reasonable voice quality down to under 30 kbps and it’s compute overhead is acceptable on available hardware.
The release a couple of months back of the Skype v4.o client for Windows was noteworthy as the introduction of their in-house developed SILK codec. Earlier today during an eComm 2009 presentation Jonathan Christensen, Skype GM Audio & Video, announced that SILK was being released under a royalty free license.
SILK was notable as being capable of narrowband (8KHz), wide band (16KHz) and super-wideband (24KHz) sample rates. Skype claims the codec dynamically adapts both sample rate and bitrate in response to variable network quality. They have published a PDF with a very general overiew of codec performance expressed in terms of bitrates, CPU requirements and MOS scores.
Apparently SILK offers not only excellent audio quality, but is also better suited to embedded applications. More dependent upon fixed point calculations it’s better suited to Skype clients running on hardware other than PCs. That makes perfect sense since Skype is showing up on lots of hardware these, especially now that there’s the Skype Lite Java client for many cell phones.
The codec is presently only available in Skype 4 Beta for Windows.