Support for OpenH264 v1.6.0 codec

[ming]

Support for the open source implementation of H.264 codec from ​http://www.openh264.org.

Requirement:

• OpenH264 library version 1.6 release (download ​here)
• To avoid conflict, it is recommended to cleanly remove ALL previous/other versions of OpenH264 on your machine, especially if you previously used OpenH264 version 1.0 following the ticket #1758.

Implementation features:

• Constrained Baseline, default level=30 (0x1e)
• packetization modes: 1, 0
• key frame request and indication
• obey remote's fmtp

Notes:

• currently transmission is hard coded to use only single NAL (packetization mode 0) regardless of remote's fmtp for interop reason. The same is also done in ffmpeg wrapper.
• whole frame for file encoding is implemented but currently doesn't work

Below are the steps to use the codec:

For GNU targets:

1. Build the OpenH264 library and install it to a directory (with "make install"). By default it installs to /usr/local. You need to modify the Makefile to install it to different location (=prefix).
2. Run PJSIP's configure. If you specify alternate location (prefix) to OpenH264 installation, specify the location with --with-openh264 option. E.g.:

   ./configure --with-openh264=/home/user/opt
   

3. Add this to your config_site.h:

   #define PJMEDIA_HAS_OPENH264_CODEC		1
   

4. If you specify an alternate OpenH264 location, add the location path (the path which contains libopenh264*.dylib) to your OS dynamic library path. For example, on Mac:

   export DYLD_LIBRARY_PATH=/Users/teluu/openh264-1.6-mac/lib:$DYLD_LIBRARY_PATH
   

For Visual Studio:

1. Build the OpenH264 library with MinGW make & gcc, and install it to a directory (with "make install"). By default it installs to /usr/local. You need to modify the Makefile to install it to different location (=prefix).
2. Create openh264.lib from openh264.def, note that the static lib libopenh264.a outputted by MinGW gcc cannot be used by VS, so we are going to use the dynamic lib version instead:
   1. open 'Visual Studio command prompt', e.g: Win Start Menu -> MS VS 2005 -> VS Tools -> VS 2005 Command Prompt
   2. change dir to OpenH264 source root directory
   3. run "lib /def:openh264.def", this will create openh264.lib, copy this file to the OpenH264 installation directory
   4. rename or copy libopenh264.dll to openh264.dll and put it in the system path
3. Add OpenH264 include and library installation paths to Visual Studio search path settings.
4. Add this to your config_site.h:

   #define PJMEDIA_HAS_OPENH264_CODEC		1
   

For iOS:

1. Follow the guidance for GNU targets above.
2. Include libopenh264.a and iOS-SDK's libstdc++.dylib to application project in XCode.

For Android:

1. Build the OpenH264 library according to the instructions provided in README.md at the OpenH264 directory. Modify the Makefile to install it to different location (modify the "prefix") and run "make install".
2. Copy libopenh264.so to your Android application library directory (such as libs/armeabi).