SoundTouch source code package contains example project that compiles SoundTouch into Android native library, and gives an example JNI interface that can invoke the native SoundTouch routines from an Android application.
Software prerequisites:
Hint: As setting up all the components and settings for an Android SDK/NDK environment requires fair effort, I recommend creating a dedicated clean Virtual Machine environment and installing all the Android developer tools into there. Having the Android developer environment setup in dedicated Virtual Machine allows keeping all these settings isolated from your other PC operations, and eases creating full backup snapshots of your development environment.
Compiling
To compile the SoundTouch library source codes into an Android native library, open Cygwin/bash shell and go to directory "soundtouch/source/Android-lib/jni" and invoke the NDK compiler as follows:
$NDK/ndk-build
This will build the ARMv5 and ARMv7 versions of SoundTouch library (including also the example JNI interface, see below) into "libs" folder.
Notice that in order for Cygwin/bash to locate the NDK compile scripts, you'll need to have the location of the NDK installation defined in environment variable "NDK". That's easiest done by adding the NDK path definition at end of your ~/.bash_profile file, for instance as follows:
NDK=/cygdrive/d/Android/android-ndk-r6
Android NDK builds default compilation for ARMv5 CPU generation that works in all ARM-based Android devices.
This has a pitfall though: For ideal sound quality SoundTouch should be compiled to use floating-point algorithms, however, some low-end Android devices do not have floating-point hardware in their CPU, and hence the default ARMv5 compilation uses software-emulation for floating-point calculations instead of hardware floating-point instructions to support also these low-end devices.
The floating point software-emulation is however several tens of times slower than real hardware-level floating-point calculations, making floating-point-intensive applications such as SoundTouch infeasible for low-end devices.
As workaround, the SoundTouch Android compilation builds two separate versions of the library:
These two library compilations are defined in file "jni/Application.mk" and results in automatically building two separate library targets under the "libs" directory. As far as you include both these compiled library versions into your application delivery, the Android environment can automatically select the right library version based on the customer device capabilities.
Please yet be aware that depending on capabilities of the Android devices you will need to provide the SoundTouch routines with samples in either integer or floating-point format, so build your interface routines to take this into account.
The NDK tools build SoundTouch c++ routines into a native binary library, while Android applications are written in Java language. To call SoundTouch and other c/c++ routines from an Android java application code, you'll need to use Java Native Interface (JNI).
The SoundTouch source code package provides an example how to use JNI to call native c++ routines from a Java class through the following source code file pair:
Feel free to examine and extend the provided cpp/java source code example file pair to implement and integrate the desired SoundTouch library behavior into your Android application.
Copyright © Olli Parviainen