...an audio engine for Android written in C++, using OpenSL for low latency performance. The engine has been written for the MikroWave synthesis/sequencing-application and works from API level 9 (Android 2.3/Gingerbread) and up.

The engine provides an architecture that allows you to work with audio within a musical context. It is easy to build upon the base classes and create your own noise generating mayhem. A few keywords describing the out-of-the-box possibilities are:

• tempo-based sequencing
• support for alternate time signatures
• multi-channel audio output
• effect chains operating on individual channels
• on-the-fly audio synthesis
• sample-based playback (e.g. drum machines)
• bouncing output to WAV files, either live or "offline"

Though the library is written in C++ (and can be used solely within this context), the library is built using JNI (Java Native Interface) allowing its methods to be exposed to Java while still executing in a native layer outside of the Dalvik/ART VM. In other words : high performance of the engine is ensured by the native layer operations, while ease of development is ensured by keeping application logic / UI within the realm of the Android Java SDK.

If you intend to use the MWEngine for sample based playback / use the built-in synthesizer and processors you will not need to write any additional C++ code. If you however intend to create your own processors or synthesis routines (which is fun!), you must write them in C++, but can rely on SWIG for making them usable in Java.

It is important to note that when a Java object finalizes (i.e. all its references are broken and is garbage collected), the destructors of the native objects are invoked, which can lead to unpredictable results if you happen to overlook this! As such, audio engine objects such as effects processors or events that are created on the Java side, must also hold strong references during their lifecycle.

The makefile (/jni/Android.mk) has been written to build the library by default using SWIG, making it available to both C++- and Java codebases. The SWIG interface file (jni/mwengine.i) includes all the engine's actors that should be exposed to Java.

Those of a Unix-bent can immediately run the build.sh-file in the /src-folder, just make sure ANDROID_NDK_ROOT points to the correct installation directory on your system!

For the unfortunate on Windows, adjusting the shell script to a .BAT-file shouldn't be too troublesome.

This repository is constantly being updated and as such so is the documentation. You can view the Wiki (which will document the basic engine architecture) here:

https://github.com/igorski/MWEngine/wiki

Note you can always view the contents of the header files to get more details about the inner workings of each class.

The repository contains an example Activity that is ready to deploy onto any Android device/emulator supporting ARM-, ARMv7-, x86- or MIPS-architecture and running Android 2.3 or higher. The example will demonstrate how to quickly get a musical sequence going using the library.

To install the demo : first build the library as described above, and then run the Ant build script to deploy the .APK unto an attached device/emulator (note that emulated devices can only operate at a sample rate of 8 kHz!). This requires both the Android NDK and the Android SDK.

Be sure to point towards the installation locations of these in both the build.sh-file and the local.properties-file.