I decided to build home PBX based on Asterisk VoIP server running on my Raspberry Pi device. One of the reasons for this was ability to build cheap GSM gate for home use using chan_dongle. But one of the problems i have found was lack of g.729 codec for the Asterisk on ARM.
On Intel platform it is possible to use codecs from asterisk.hosting.lv or to buy commercial codec from Digium. Unfortunately its not the case for the ARM. So i decided to see if it possible to port some existing g.729 codec.
Project asterisk-g72x is only Open Source g.729 for Asterisk implementation i am aware of. Internally it is using 2 libraries:
- IPP from Intel
- Or ITU based reference code.
It is not possible to compile recent IPP versions on ARM and a lot of ASM code making porting of it problematic. ITU g.729 code is on a plain C, but is painfully slow. It compiles on ARM, but performance is terrible. Asterisk eating 100% of CPU on recoding and drops frames. So it was not an option. So i decided to find alternative codec. In the net i found 2 Open Source projects with g.729 implementation suitable for ARM
- Experimental version of G.729 codec for ARM device. It seems to be ITU source code with ARM assembler code for some operations.This code also using many global variables so is not ready for multi-thread software like asterisk without additional changes. Also there are issues open from 2011 without any reaction from developers.
- Bcg729. It is a software G729A encoder and decoder library written in C, developed by Belledonne Communications, the company supporting the Linphone project. It was written from scratch and is NOT a derivative work of ITU reference source code in any kind.
BCG 729 also supports concurrent channel encoding/decoding for multi-call applications such as Asterisk. I was able to adopt bcg729 for use with asterisk-g72x project, instead of slow ITU code. If you want to test it – use my BitBucker fork. I will post benchmarks later, but now i see about 15-20% CPU load on g.729 encoding with Asterisk, so it should be able to support 4-5 concurrent channels in time.