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118 lines
6.8 KiB
HTML
118 lines
6.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<title>SoundTouch in Android</title>
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<meta http-equiv="Content-Type"
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content="text/html; charset=windows-1252">
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<meta http-equiv="Content-Language" content="en-us">
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<meta name="author" content="Olli Parviainen">
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<meta name="description"
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content="Readme file for SoundTouch library Android compilation">
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<style> <!-- .normal { font-family: Arial }
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--></style>
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</head>
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<body class="normal">
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<hr>
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<h1>SoundTouch in Android</h1>
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<hr>
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<h2>Compiling SoundTouch for Android</h2>
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<p>SoundTouch source code package contains "Android-lib" example project that compiles SoundTouch
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source codes into Android native library, and gives an example of JNI interface
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for invoking
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the native SoundTouch routines from an Android application written in Java.</p>
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<p style="font-weight: 700">Software prerequisites:</p>
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<ul>
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<li>Android SDK environment for developing your own Android application. Visit the <a href="http://developer.android.com/index.html">Android developers' site</a>
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for more information about the Android SDK and developing Android applications.</li>
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<li>Android NDK compiler kit for compiling native library binaries. The Android NDK
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is <a href="http://developer.android.com/tools/sdk/ndk/index.html">
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available for download</a> at the Android developer tools site.</li>
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<li>In case you're working in Windows environment, install
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<a href="http://cygwin.com/install.html">
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Cygwin</a> to run the Android NDK/SDK compiler scripts</li>
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<li>Latest SoundTouch source code package available at <a href="http://soundtouch.surina.net/sourcecode.html">
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soundtouch.surina.net</a>.</li>
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</ul>
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<p><b>Hint: </b>As installing and configuring all the components for an Android SDK/NDK
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environment requires fair effort, it's good idea to create a dedicated Virtual
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Machine environment for the Android development environment installation.
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Having the Android developer environment setup in dedicated Virtual Machine
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allows keeping all these settings isolated from your other PC operations, and
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eases taking backup snapshots of your full development environment.</p>
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<p><b>Compiling</b></p>
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<p>
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To compile the SoundTouch library source codes into an Android native library,
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open Cygwin/bash shell, go to directory <b>"soundtouch/source/Android-lib/jni"</b> and invoke the NDK
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compiler with following command:</p>
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<pre> $NDK/ndk-build</pre>
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<p>This will build the ARMv5 and ARMv7 versions of SoundTouch library (including
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also the example JNI
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interface, see below) into the "libs" subdirectory.</p>
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<p>Notice that to allow Cygwin/bash to locate the NDK compile scripts, you
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need to define the location of the NDK installation defined in environment
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variable "NDK". That's easiest done by adding the NDK path definition at end of
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your <b>~/.bash_profile</b> file, for instance as follows:</p>
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<pre> NDK=/cygdrive/d/Android/android-ndk-r6</pre>
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<hr />
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<h2>
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Android floating-point performance considerations</h2>
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<p>
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Default build target for
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Android NDK is ARMv5 CPU generation, as that works in
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all ARM-based Android devices.<p>
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This has a pitfall though: For ideal sound quality SoundTouch should be compiled
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to use floating-point algorithms, however, all low-end Android devices do not
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have floating-point hardware in their CPUs, and hence the default ARMv5 compilation uses software-emulation for floating-point calculations instead of
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hardware floating-point to allow running the binary executables also in low-end devices.<p>
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The floating point software-emulation is however several tens of times slower
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than real hardware-level floating-point calculations, making
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floating-point-intensive applications such as SoundTouch infeasible with low-end
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devices.<p>
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As workaround, the SoundTouch Android compilation builds two separate versions
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of the library:<ul>
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<li>ARMv5 version that compiles SoundTouch using integer algorithm version. The integer
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algorithm version compromises the sound quality but provides good performance also
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with low-end
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devices without hardware floating-point support in the CPU level.</li>
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<li>ARMv7 version that compiles SoundTouch using hardware floating-point algorithms.
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These algorithms provide ideal sound quality yet do not work in simpler CPU
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models.</li>
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</ul>
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<p>
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These two library compilations are already defined in file "<b>jni/Application.mk</b>"
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so that these two separate library targets are automatically built under the "<b>libs</b>"
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directory. As far as you include both these compiled library versions into your
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application delivery, the Android devices can automatically select the right
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library version based on the available device's capabilities.<p>
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Please yet be aware that depending on capabilities of the Android devices you
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will need to provide the SoundTouch routines with samples in either integer or
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floating-point format, so build your interface routines to take this into
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account.<hr />
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<h2>
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Calling SoundTouch native routines from Android application</h2>
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<p>The NDK tools build the SoundTouch c++ routines into a native binary library, while
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Android applications are written in Java language. To call the SoundTouch and other c/c++
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routines from an Android java application code, you'll need to use Java Native
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Interface (JNI).</p>
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<p>
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The SoundTouch source code package provides source code example how to
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use JNI to call native c++ routines from a Java class through the following
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source code file pair:<ul>
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<li><b>Android-lib/jni/soundtouch-jni.cpp</b>: This file contains c/c++ routine that
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calls SoundTouch library routine to return the library version string to the main
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Android application. The NDK compiles this file along with the SoundTouch
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routines into the native binary library.</li>
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<li><b>Android-lib/src/net/surina/soundtouch/SoundTouch.java</b>: This file provides
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a Java interface class to load the native library and to invoke the native routine implemented in
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the file <b>soundtouch-jni.cpp</b></li>
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</ul>
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<p>
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Feel free to examine and extend the provided cpp/java source code example file pair to
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implement and integrate the desired SoundTouch library capabilities into your Android application.</p>
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<hr />
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<p style="text-align: center"><i>Copyright © Olli Parviainen</i></p>
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