Internet Speech Audio Codec
internet Speech Audio Codec ( iSAC ) is an openly documented, royalty-free broadband speech codec originally developed by Global IP Solutions (GIPS). It is suitable for IP telephony applications and streaming audio . The coded blocks must be packaged in a suitable protocol for transmission, for example RTP .
In contrast to the iLBC , this codec was proprietary , i.e. the implementation had to be licensed by GIPS and the algorithm was not accessible. As a result of the acquisition of GIPS by Google Inc. , the process is available to everyone free of license fees for unconditional use and the reference implementation is distributed as free software under the terms of a BSD-like license .
It is used in Gizmo5 , Google Talk and possibly soon in Microsoft products (MSN and Microsoft Office Real-Time Collaboration, RTC). It used to be used in Skype .
iSAC is a broadband codec with a variable bit rate that can adjust its bit rate between 10 and 32 kbit / s.
Parameters and characteristics
- Sampling frequency of 16 kHz
- variable bit rate with adaptable packet size (10 to 32 kbit / s or 30 to 60 milliseconds)
- Complexity comparable to G.722.2 with comparable bit rates
- Delay in the procedure: packet size plus 3 milliseconds