Tuesday, March 2, 2010

An AMBE open source compatible codec?

First some history:

Depending on your point of view, Jon Lech Johansen is either your hero or adversary. To the copyright industry, Jon Lech Johansen has been a detriment to their policy of control since the advent of DeCSS (Decrypt Content Scrambling System.)

At the age of 15, “DVD Jon” wrote a computer program that allowed users to copy DVDs. Then he posted it on the Internet. A Norwegian private school awarded him a prize for making an outstanding contribution to society. The Norwegian government indicted him.

Jon spent 3 long years in the Norwegian courts proving his innocence. The American movie industry pressured the Norwegian Economic Crime Unit to press charges against Jon Lech Johansen in 2000 for allegedly bypassing the CSS copy protection on DVDs.


Early on; Bruce Perens, K6BP, amateur radio and open source advocate voiced concerns about D-Star’s use of a proprietary vocoder. Asking; does it really fit into the spirit of the hobby? Bruce makes a strong argument that an Open Source vocoder needs to be developed.

In May 2008, he announced that he will investigate the development of an alternative codec. The Codec2 Project: Next-Generation Audio Codecs and Vocoders for Two-Way Radio.

In August 2009 David Rowe, VK5DGR, began designing and implementing a replacement codec under the GPL.

“Proprietary codecs typically have small, novel parts of the algorithm protected by patents. However proprietary codecs also rely heavily on large bodies of public domain work. The patents cover perhaps 5% of the codec algorithms. Proprietary codec designers did not invent most of the algorithms they use in their codec. Typically, the patents just cover enough to make designing an interoperable codec very difficult. These also tend to be the parts that make their codecs sound good.”


The AMBE codec was patented [6] (US: 6199037, US Classification 704/208; 704/222; 704/230, International Classification G10L 1106; G10L 1902)on Dec 4, 1997 and issued in Mar 6, 2001 to John C. Hardwick of Digital Voice systems, Inc. [Patents last 20 years from the date of application]

Two open source compatible codec’s that come to mind:

Thomson Multimedia and Fraunhofer Society originally controlled the patents and licensing of the MP3 audio codec. Tip-toeing around the patented parts of the algorithms the LAME encoder was developed as free software application used to encode audio into the MP3 file format.

The DivX codec (used to compress lengthy video segments into small sizes while maintaining relatively high visual quality.) was actually an attempt by the now defunct U.S. retailer Circuit City to develop a video rental system requiring special discs and players.

The Xvid codec became a primary free and open source competitor offering comparable quality. It too was developed by tip-toeing around the patented parts of the DivX algorithms.

Think about it...... Do you like your freedoms? Thank those who have taken the time reverse engineered something. Welcome those types with open hands to the hobby. Those types of experimenters are just what this hobby once was and still can be.

{Update May 2010}
Interestingly enough the Digital Speech Decoder and xMBE codec library - can decode and recover the audio from P25 (Phase 1) IMBE, as well as Mototrbo (AMBE+2).

Is the reason the AMBE codec of D-Star isn't supported because it might cut into Robin Cutshaw, AA4RC's DV Dongle sales?

2 comments:

ws4e said...

>was actually an attempt by the now defunct U.S. retailer Circuit City

Actually, its just an unfortunate coincidence that they used the same name. They have nothing to do with each other in reality.

Anonymous said...

i wish we had an open vocoder to play with.