Building under OSX is similar to building under linux, but there are some additional steps that need to be performed to produce a working app-bundle.

For the following instructions, I'm assuming you will be placing everything in:
/Users/<yourusername>/Dev/

1/ DEPENDENCIES
Using Macports, most of the appropriate dependencies can be installed by:

$ sudo port install subversion git libtool libsamplerate sox portaudio cmake

It should be fairly similar using HomeBrew, but you will need to replace all the /opt/ paths in the following instructions.

1.1/ HAMLIB 
First, we will need to build hamlib from source, as we need hamlib to be statically compiled (Macports won't do this..)

$ git clone git://git.code.sf.net/p/hamlib/code hamlib-code
$ cd hamlib-code

You will now need to edit line 12 of autogen.sh, to change "libtoolize" to "glibtoolize"

$ ./autogen.sh
$ ./configure --disable-shared --prefix /Users/<your-username-here>/Dev/hamlib
$ make
$ make install

You should now have an installation of hamlib in ~/Dev/hamlib

Just in case you have hamlib installed via Macports, it may be a good idea to run
$ sudo port deactivate hamlib

1.2/ WXWIDGETS
To be able to produce an appbundle, we need wxWidgets to be build statically. Again, Macports won't do this out of the box.

Edit the wxWidgets-3.0 port file using:
$ sudo port edit wxWidgets-3.0

and add the following to the bottom of the file:

variant static description { build a static version of the libraries with some other options... } {
    configure.args-append       --enable-std_iostreams
    configure.args-append       --disable-shared
    configure.args-delete       --with-sdl
    configure.args-delete       --with-opengl
    set installtype release-static
}

Now you can build and install a static variant of wxWidgets with:
$ sudo port install wxWidgets-3.0 +static

Note: This will probably break anything else which is using wxWidgets. Once you have finished building FreeDV, you may
want to go back to the dynamically compiled version using:
$ sudo port install wxWidgets-3.0

HomeBrew Users: Anyone know how to do the above?

1.3/ CODEC2 LIBRARIES
The FreeDV CMake procedure will automatically checkout and compile Codec2.
If you want to build and install your own copy (i.e. for access to the command-line tools), you can do so:

$ wget http://files.freedv.org/codec2/codec2-0.4.tar.gz
or
$ svn checkout https://svn.code.sf.net/p/freetel/code/codec2-dev/

$ cd codec2-0.4
or 
cd codec2-dev
$ mkdir build_osx && cd build_osx
$ cmake ../ && make
$ sudo make install

3/ BUILDING FREEDV 
Get the FreeDV source by either:

Getting the current 'stable' release (1.0):
$ wget http://files.freedv.org/freedv/freedv-1.0.tar.gz
$ tar -xzf freedv-1.0.tar.gz

or

Checking the latest revision out from SVN:
$ svn checkout https://svn.code.sf.net/p/freetel/code/freedv-dev/

$ cd freedv-1.0
or 
$ cd freedv-dev

$ mkdir build_osx && cd build_osx

Assuming you are intending on building Codec2 as part of the build process, run:

$ cmake -DWXCONFIG=/opt/local/Library/Frameworks/wxWidgets.framework/Versions/wxWidgets/3.0/lib/wx/config/osx_cocoa-unicode-static-3.0 -DCMAKE_EXE_LINKER_FLAGS="-L/opt/local/lib" -DHAMLIB_INCLUDE_DIR=../../hamlib/include -DHAMLIB_LIBRARY=../../hamlib/lib/libhamlib.a ../

Then, build FreeDV:
$ make

The build process will create an appbundle (FreeDV.app) and a compressed disk image (FreeDV.dmg) in ./build_osx/src
Move these to wherever you want, and run!

Happy DVing!

Acknowledgements:
A big thank you to Mooneer Salem, K6AQ, for walking me through this process, and figuring out how to solve the wxWidgets and Hamlib issues.

Please e-mail any corrections to either the digitalvoice google group list, or myself, at:
vk5qi(at)rfhead.net
Mark Jessop VK5QI

