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118 lines
6.9 KiB
HTML
118 lines
6.9 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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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 example project that compiles SoundTouch
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into Android native library, and gives an example JNI interface that can invoke
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the native SoundTouch routines from an Android application.</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. For more
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information about the Android SDK and developing the applications please visit
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the <a href="http://developer.android.com/index.html">Android developers' site</a>.</li>
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<li>Android NDK compiler kit to create native library compilations. Follow this link
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to <a href="http://developer.android.com/tools/sdk/ndk/index.html">
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download the Android NDK</a> from the Android developer tools site.</li>
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<li>In case you're working in Windows environment, you'll need <a href="http://cygwin.com/install.html">
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Cygwin</a> to invoke the Android NDK/SDK compile 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 setting up all the components and settings for an Android SDK/NDK
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environment requires fair effort, I recommend creating a dedicated clean Virtual
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Machine environment and installing all the Android developer tools into there.
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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 creating full backup snapshots of your 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 and go to directory <b>"soundtouch/source/Android-lib/jni"</b> and invoke the NDK
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compiler as follows:</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 "libs" folder.</p>
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<p>Notice that in order for Cygwin/bash to locate the NDK compile scripts, you'll
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need to have 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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Android NDK builds default compilation for ARMv5 CPU generation 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, some low-end Android devices do not
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have floating-point hardware in their CPU, and hence the default ARMv5 compilation uses software-emulation for floating-point calculations instead of
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hardware floating-point instructions to support also these 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 for 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 algorithms. 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 whose CPUs do not have hardware floating-point support</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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versions.</li>
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</ul>
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<p>
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These two library compilations are defined in file "<b>jni/Application.mk</b>"
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and results in automatically building two separate library targets 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 environment can automatically select the right
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library version based on the customer device 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 SoundTouch c++ routines into a native binary library, while
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Android applications are written in Java language. To call 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 an 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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uses SoundTouch library routines 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 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 invoke the native routine implemented in file <b>soundtouch-jni.cpp</b>
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for reading the SoundTouch library version string from the Android Java
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application code.
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</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 behavior 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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