This means configure did not detect it, maybe you installed after you ran configure or it's an error in the Ubuntu package ?

On Wednesday, October 14, 2015, sunil more <sunil.more64@yahoo.in> wrote:
Hello All,
I am trying to compile freeswitch latest commit on Ubuntu Server and I am getting stuck while compiling mod_shout. It asked me for adding dependency libmpg123-dev. I have this lib package already installed on my machine. However i still get stuck over this error. Please help me.
Operating system:
Distributor ID: Ubuntu
Description: Ubuntu 14.04.3 LTS
Release: 14.04
Codename: trusty

Error:
making all mod_shoutmake[4]: Entering directory `/usr/local/src/freeswitch/src/mod/formats/mod_shout'
Makefile:895: *** You must install libmpg123-dev to build mod_shout.  Stop.
make[4]: Leaving directory `/usr/local/src/freeswitch/src/mod/formats/mod_shout'
make[3]: *** [mod_shout-all] Error 1
make[3]: Leaving directory `/usr/local/src/freeswitch/src/mod'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/usr/local/src/freeswitch/src'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/usr/local/src/freeswitch'
make: *** [all] Error 2

Regards,
Sunil More