How to add custom media codec to pjsip

Hi, in this post, I will show you how to add a custom codec to pjsip 2.2.1

Introduction:

http://www.pjsip.org

pjsip is a very strong and widely use in voip. you can combine pjsip with kamailio, stund, turn server, freeswitch to build chat application like Skype with many well feature like message, call, conversation.v.v.

http://www.opus-codec.org

opus is a lightweight media codec with very good quality but also cost minimum bandwidth (you can customize it bitrate yourself)

to port opus codec you should choose a codec and follow it config (gsm for example)
(This tutorial I read from http://www.piemontewireless.net/, but now, this link is no longer exist)
A little bit you need to know about pjsip build system (make file)
pjsip use a set of make files to build, if you familiar with gnumake, it’s very easy to understand pjsip. but if you are not, here are some tips to help you easily maintain pjsip and solved bug when buid

• notice about “build” dir, it’s contain make file you need to config
• file *.in is input file, config init, run config again and it will generate *.mak file base on *.in
• autoconf acconfigure.ac > acconfigure

Porting opus with pjsip interface

1. Add opus source code:

1.1 you must write api for opus to work with pjmedia, ex: (view resource file for more)

PJ_DECL(pj_status_t) pjmedia_codec_opus_init(pjmedia_endpt *endpt);
PJ_DECL(pj_status_t) pjmedia_codec_opus_deinit(void);

1.2 after write opus.h and opus.c file for pjmedia. put it in:

header file: pjmedia/include/pjmedia-codec
source file: pjmedia/src/pjmedia-codec

1.3 add opus source to third_party.
1.4 int third_party/build create new opus dir, write Makefile and config for all c file in opus

2. Config pjsip build system, find appropriate place to port this code, often after g7221 config

2.1 aconfigure.ac

line 846:
dnl # Include opus codec
AC_SUBST(ac_has_opus_codec)
AC_ARG_ENABLE(opus_codec,
AC_HELP_STRING([--enable-opus-codec],
[Enable OPUS support (derived from ITU implementation).]),
[ac_has_opus_codec=1]
AC_DEFINE(PJMEDIA_HAS_OPUS_CODEC,1)
AC_MSG_RESULT([Checking if opus codec is disabled...no]),
[ac_has_opus_codec=]
AC_MSG_RESULT([Checking if opus codec is disabled...yes])
)

2.2 pjsip/build.mak.in

ifeq (@ac_has_opus_codec@,1)
APP_THIRD_PARTY_LIB_FILES += $(PJ_DIR)/third_party/lib/libopuscodec-$(LIB_SUFFIX)
ifeq ($(PJ_SHARED_LIBRARIES),)
APP_THIRD_PARTY_LIBS += -lopuscodec-$(TARGET_NAME)
else
APP_THIRD_PARTY_LIBS += -lopuscodec
APP_THIRD_PARTY_LIB_FILES += $(PJ_DIR)/third_party/lib/libopuscodec.$(SHLIB_SUFFIX).$(PJ_VERSION_MAJOR) $(PJ_DIR)/third_party/lib/libopuscodec.$(SHLIB_SUFFIX)
endif
endif

2.3 pjmedia/build/os-auto.mak.in

AC_HAS_OPUS_CODEC=@ac_has_opus_codec@
...
ifeq ($(AC_HAS_OPUS_CODEC),1)
export CFLAGS += -I$(THIRD_PARTY)/opus/include -DPJMEDIA_HAS_OPUS_CODEC=1
export CODEC_OBJS += opus.o
endif
...

2.4 third_party/build/os-auto.mak.in

ifeq (@ac_has_opus_codec@,1)
DIRS += opus
endif

2.5 pjmedia/include/pjmedia-codec.h

#include <pjmedia-codec/opus.h>

2.6 pjmedia/include/pjmedia/codec.h

PJMEDIA_RTP_PT_OPUS = 20

2.7 pjmedia/include/pjmedia-codec/config.h

/**
 * Unless specified otherwise, OPUS codec is not included by default.
 */
#ifndef PJMEDIA_HAS_OPUS_CODEC
#   define PJMEDIA_HAS_OPUS_CODEC    1
#endif

2.8 pjmedia/include/pjmedia-codec/config_auto.h

/* OPUS codec */
#ifndef PJMEDIA_HAS_OPUS_CODEC
#define PJMEDIA_HAS_OPUS_CODEC 1
#endif

2.9 pjmedia/include/pjmedia-codec/config_auto.h.in

/* OPUS codec */
#ifndef PJMEDIA_HAS_OPUS_CODEC
#undef PJMEDIA_HAS_OPUS_CODEC
#endif

2.10 pjmedia/src/pjmedia-codec/audio_codecs.c

#if PJMEDIA_HAS_OPUS_CODEC
    status = pjmedia_codec_opus_init(endpt);
    if (status != PJ_SUCCESS) {
        return status;
    }
#endif /* PJMEDIA_HAS_OPUS_CODEC */

3. run config and build pjsip

autoconf acconfigure.ac > acconfigure
configure --with-ssl --enable-opus-codec
make-dep
make