Which is the best SIP compatible codec type for Android

android rest voip sip sip-server
Foyzul Karim picture Foyzul Karim · Mar 31, 2011 · Viewed 12.6k times · Source

I want to develop a Android App which will use a SIP Server of my client. My client is exposing couple of REST API from the SIP server for communicating with the apps.

I want to know which would be the best codec type for this app?

Basically, I want to create a SIP-Stack and send the SIP Packets to the Server. So, there should be a coding and decoding system for the packets. My client prefers 16 kb/sec but I am not sure which should I use.

Answer

Hank Karl picture Hank Karl · Apr 1, 2011

As others have said, SIP does not transfer audio or video. Although in theory, you can send data over any transport, including ATM, analog lines, a DS0, etc, in the real world, RTP is the most common. RTP (Real Time Protocol) and RTCP (Real Time Control Protocol) or SRTP (Secure RTP) usually carry the audio and video.

As far as codecs go, you will be limited by what your server supports. Here are a few common codecs and some pros and cons of each.

G.711 - Toll quality (ie good as a good analog phone line, or even a bit better). "Universal" in that virtually every device supports G.711. Takes a lot of bandwidth, it doesn't really compress data (G.711 is a "compander"). The baseline G.711 is pretty bare-bones (its really a couple of look up tables). Appendix I adds packet loss concealment (PLC) and Appendix II adds silence suppression and comfort noise generation.

GSM - used on cellphones, sounds ok, good PLC, good compression

G.729A - widely used, near toll quality, good compression (8Kbps)

G.723.1 - widely used, almost as good as G.729, better compression (4-5Kbps)

G.722 - sounds better than G.711, wideband (twice the audio bandwidth of G.711 or an analog call), same bandwidth used on the line as G.711

GIPS - various implemnetations exist, one is free. IIRC, uses about 13.5Kbps on the line, sound is not as good asG.723.1 (but this is a perceptual metric, YMMV) Takes a lot of processor.

All the codecs use some processor and other system resources, as a rule of thumb the more aggressive the codec (the smaller the bandwidth) the more processor used. Also, all of these particular codecs are lossy codecs--they lose some of the data. This means that there is compression, not that portions of the audio are dropped due to poor routing and poor line quality. Much like an MP3 is considered a LOSSY codec while FLAC is considered Lossless. If you're interested the following wikipedia article explains in further detail: http://en.wikipedia.org/wiki/Lossy_compression

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