For the Best Voice and Music, Will it be Opus or AAC?

By Doug Mohney September 25, 2012

Buried under the onslaught of iPhone 5 madness last week was finalization of the open-source Opus codec as an IETF codec. Audiophiles and open source gurus are enthusiastic and happy, but the Fraunhofer "Full HD" voice AAC family is already shipping on Apple iOS and Android devices. 

Will licensed beat open this time around?

Opus can trace its roots to not one, but two different wideband codecs. One part of the family tree traces back to the open-source Speex project and the other to Skype  and the SILK codec, with both sides lining up to propose a single standard to the IETF over three years ago.

The IETF RFC 6716 final specification became official on September 11, 2012, with reference code out the door the following day.  

Backers of the standard include Mozilla, Microsoft via its Skype subsidary, Xiph.Org, Octasic, Broadcom and (of course) Google. Opus is designed to be highly flexible, able to carry both voice and music over bit rates ranging from 6 kbps to 512 kbps in mono and stereo formats, with a sound range from 8 kHz narrowband to "Fullband" 48 kHz.

Royalty free and open source, Opus is capable of replacing at least six proprietary codecs covering from iLBC and G.711 codecs designed to carry narrowband voice all the way up through CD-and-better stereo music streaming using MP3 and AAC.

Opus is a mandatory-to-implement codec for WebRTC real time communications, so you'll see a lot of it in the programming community.

A single, open source, royalty-free codec (or at least fewer) would make life easy for programmers and device manufacturers, since they wouldn't have to support a lengthy-and-growing laundry list of code. Not to mention having to worry about license fees and having to keep track of per-device fees.

For the long term, Opus looks like a good bet. But it will have to wrestle with the likes of the Fraunhofer AAC codecs on mobile devices and smart TVs.

 Fraunhofer, the creator of the MP3 standard, have licensed what it has dubbed "Full HD voice" AAC codecs to Apple and Google for incorporation into iOS and Android devices. The technology company likes to boast AAC's use in Apple FaceTime with millions of users for video calling on iPads, iPhones and Macintosh clients. Numbers for Android apps using AAC aren't kicking around anywhere, but Fraunhofer has demonstrated the ability to make AAC phone calls between off-the-shelf Android smartphones over LTE  without breaking a sweat.

When the smoke clears, AAC is on a lot of end-point devices, but you have to pay for its use. The big cog that may prevent AAC from getting into the "mainstream" is transcoding between the format and lower quality formats. Companies involved with translating between narrowband and wideband codecs may not want to shell out the money to support AAC, preferring to support Opus because it's royalty free and open source. 

 Fraunhofer would likely argue that if you're in an all-SIP world, you don't have to transcode, but simply default to another codec if AAC isn't available between two clients. But if Opus is royalty free in the first place, maybe it becomes the default for voice, while AAC sticks around because of all the music content – such as iTunes songs – it can play back.

Edited by Jamie Epstein

Contributing Editor

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