Support for Libyuv

[riza]

Support for libyuv library which provides YUV scaling and conversion functionality (​https://code.google.com/p/libyuv/).

Requirement:

• Libyuv library. For building the library, we recommend using the steps described ​here.

This implementation will provide video scaling and conversion functionality.

Below are the steps to use the codec:

For GNU targets:

1. Build Libyuv library. Make sure to execute the Release build step (ninja -j7 -C out/Release). The library will be built on ([libyuv_dir]/out/Release).
2. Run PJSIP's configure and specify the Libyuv folder using --with-libyuv option. E.g:

   ./configure --with-libyuv=/home/user/src/libyuv
   

For iOS targets:

1. Build Libyuv library. Make sure to execute the Release build step (ninja -j7 -C out_ios/Release-iphoneos libyuv_unittest). The library will be built on ([libyuv_dir]/out_ios/Release-iphoneos).
2. Run PJSIP's configure-iphone and specify the Libyuv folder using --with-libyuv option. E.g:

   ./configure-iphone --with-libyuv=/home/user/src/libyuv
   

3. Add libyuv.a to application project in XCode. For armv7 architecture, also add libyuv_neon.a to the application project.

Notes for iOS targets:

• armv7s it is still not supported because of the limitation from chromium build tools.

For Visual Studio:

1. Build the Libyuv library.
2. Add Libyuv include and library location paths to Visual Studio search path settings.
3. Add this to your config_site.h:

   #define PJMEDIA_HAS_LIBYUV		1
   

[riza]

In 4875:

Re #1776: Initial implementation of Libyuv wrapper. Supports:

• library detection via autoconf
• scaling and conversion function (from/to I420 or BGRA)