"WebRTC Native Stack is considered as a signal chain as close to the Hardware Abstraction Layer (HAL) as possible."
Getting Started
This repository involves a Step by Step Guide to Build Android App based on WebRTC Native Stack. As we all know, Android Programs run into Dalvik Virtual Machine. Native Development tool (NDK) allows users to execute some of the program using native code languages such as C/C++.
For Compilation and Building the WebRTC Library for Android, you should have to look into this refernce:
For real-time Communication and AudioProcessing in Android, I will recommend you to must visit these refernces:
NDK (Native Development Kit) includes the following features such as;
- Tool and build files needed to generate a native code base from
C/C++. - Embed consistent native libraries in application packages files (.apk files) that can be deployed on Android devices.
- Supports a number of native system header files and libraries for the Android platform.
Here you can select & download the latest or lagecy NDK package for your development platform i.e. NDK Download
NDk finds its best use to squeeze extra performance out to device, to achieve low latency or run computationally intensive applications on android platform. Here are some other reasons why we use NDK in our development;
- Easy to port libraries written in
C/C++can be easily reused on other embedded platforms. - Code protection, because the java code of apk can be easily decompiled, and the
C/C++library is difficult to reverse. - Call third-party
C/C++libraries in the NDK, because most open source libraries are written inC/C++code, such as WebRTC, TarsosDSP, Ffmpeg, OpenCV, and a lot of other machine learning stuff etc.
JNI (Java Native Interface) provides several APIs to implement the communication between Java and other languages (mainly C/C++).
Drawback: There is one of the major side effect of JNI is, The Program is no longer Cross-Platform. To make your program Cross-Platform, you must recompile the native language part in different system environments. The program is no longer absolutely secure, and improper use of native code may cause the entire program to crash. As a general rule, you should focus your local methods on a few classes. This reduces the coupling between JAVA and C.
In fact, Java and C/C++ are static type languages, the main reason that java and C cannot communicate is the problem of data types. JNI plays a role in data conversion. The corresponding relationship is shown in the following table:
To put it simply, NDK is an extension toolkit developed by JNI. It uses NDK to compile corresponding local static or shared libraries that can be run for different mobile devices (ARM, x86 ...). In order to improve the sorting efficiency and use C/C ++ in android, here are different steps for this process as follows:
1. SDK development (write java code, write code containing native keywords to start JNI)(Native Methods) .
2. JNI development (according to the JNI coding specification, write a local interaction with java Code, the role is to talk about the C/C++ data type conversion into Java can recognize).
3. C/C++ development (write business logic, or call the local API or library provided by the NDK to complete the development of specific functions).
4. NDK compilation ( Write the .mk file, compile and debug, modify the .mk file, and optimize the compilation results for the specific platform (ARM/X86).
5. SDK compilation and packaging.
Here we start with;
As we know that WebRTC implementation is done in C/C++ languages. It needs to integrate with android application via Java Native Interface(JNI). WebRTC source available at Github WebRTC Source Code as well as official WebRTC download page.
To integrate WebRTC code via JNI, first I needs setup android NDK. Download NDK from here and extract it. Main thing to consider here is, make sure NDK path is being setup in environment variables in windows i.e. see.
To test whether ndk-build is working or not, check these commands in the terminal like;
ndk-stack
ndk-build --help
Example:
Before digging into WebRTC Native Stack, If you don't have a basic understanding of NDK development, I must recommend you to follow this tutorial i.e Hello-JNI.
Following are the steps that I have followed to integrate WebRTC source code with my android application.
I have a seperated directory called webrtc inside the jni directory and added WebRTC source code for it. WebRTC source code can be cloned from github or download via official download page.
Make sure your project structure follow the same hierarchy as given above.
To call JNI based C function I need to write JNI wrappers for them. I kept the written wrappers in com_webrtc_audioprocessing_Apm_ package. Read more about JNI from here.
Following is the JNI wrapper for WebRTC Audio processing. I have maintained and updated Apm.java in my Android Project as given here;
This file includes the all the native instance method, via keyword native which denotes that this method is implemented in another language. A native method does not contain a body. These native methods shall be found in the native library loaded. Here are the list of native methods inculded inside the Apm.java class;
// apm constructor
private native boolean nativeCreateApmInstance(boolean aecExtendFilter, boolean speechIntelligibilityEnhance, boolean delayAgnostic, boolean beamforming, boolean nextGenerationAec, boolean experimentalNs, boolean experimentalAgc);
private native void nativeFreeApmInstance();
private native int high_pass_filter_enable(boolean enable);
// aec and aecm
private native int aec_enable(boolean enable);
private native int aec_set_suppression_level(int level); //[0, 1, 2]
private native int aec_clock_drift_compensation_enable(boolean enable);
private native int aecm_enable(boolean enable);
private native int aecm_set_suppression_level(int level); //[0, 1, 2, 3, 4]
private native int ns_enable(boolean enable);
private native int ns_set_level(int level); // [0, 1, 2, 3]
// agc
private native int agc_enable(boolean enable);
private native int agc_set_target_level_dbfs(int level); //[0,31]
private native int agc_set_compression_gain_db(int gain); //[0,90]
private native int agc_enable_limiter(boolean enable);
private native int agc_set_analog_level_limits(int minimum, int maximum); // limit to [0, 65535]
private native int agc_set_mode(int mode); // [0, 1, 2]
private native int agc_set_stream_analog_level(int level);
private native int agc_stream_analog_level();
// vad
private native int vad_enable(boolean enable);
private native int vad_set_likelihood(int likelihood);
private native boolean vad_stream_has_voice();
// Capture and render audio stream
private native int ProcessStream(short[] nearEnd, int offset); //Local data// 16K, 16Bits, 10ms
private native int ProcessReverseStream(short[] farEnd, int offset); // Remote data // 16K, 16Bits, 10ms
private native int set_stream_delay_ms(int delay);
// resampling
private native boolean SamplingInit(int inFreq, int outFreq, long num_channels);
private native int SamplingReset(int inFreq, int outFreq, long num_channels);
private native int SamplingResetIfNeeded(int inFreq, int outFreq, long num_channels);
private native int SamplingPush(short[] samplesIn, long lengthIn, short[] samplesOut,long maxLen, long outLen);
private native boolean SamplingDestroy();
The static initializer invokes System.loadLibrary() to load the native library "webrtc_apms" (which contains all native methods) during the class loading. It will be mapped to " libwebrtc_apms.dll " in Windows; or " libwebrtc_apms.so " in (Unix/Mac-OS X). This library shall be included in libs directory automatically after you run this command in terminal i.e. ndk-build. The program will throw a UnsatisfiedLinkError if the library cannot be found in runtime.
Starting from JDK 8, you should use "javac -h" to compile the Java program AND generate C/C++ header file called com_webrtc_audioprocessing_Apm.h as follows:
javac -h . Apm.java
The "-h dir" option generates C/C++ header and places it in the directory specified (in the above example, '.' for the current directory).
Before JDK 8, you need to compile the Java program using javac and generate C/C++ header using a dedicated javah utility, as follows. The javah utility is no longer available in JDK 10.
javac Apm.java
javah ApmJNI
Now place this header file (com_webrtc_audioprocessing_Apm.h) inside the following i.e. src/main/jni/
By using those generated library files and header files I have written JNI based C functions to preprocess and postprocess the audio data. These JNI files prefixed with com_webrtc_audioprocessing_Apm which is the java package path of the JNI wrappers.
Here is the JNI based audio processing module which is android_apm_wrapper.cpp, you can inspect this cpp-file.
I need to build a native shared library (.so) with my JNI C/C++ functions in order to call them from JAVA(with JNI wrapper). To do that I have written android make file Android.mk. Since my C/C++ functions using WebRTC library files, I have integrated them with the make file as well.
Following is the make file to build shared library Android.mk;
MY_WEBRTC_ROOT_PATH := $(call my-dir)
LOCAL_CFLAGS += -DWEBRTC_POSIX
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_processing/aec/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_processing/aecm/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_processing/agc/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_processing/ns/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_processing/utility/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_processing/vad/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_processing/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_processing/intelligibility/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_processing/transient/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_processing/beamformer/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/common_audio/vad/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/common_audio/signal_processing/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/common_audio/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/common_audio/resampler/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_coding/codecs/isac/main/source/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/modules/audio_coding/codecs/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/system_wrappers/source/Android.mk
include $(MY_WEBRTC_ROOT_PATH)/base/Android.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
# Here you can change the name of your shared library
LOCAL_MODULE := libwebrtc_apms
LOCAL_MODULE_TAGS := optional
LOCAL_LDLIBS += -llog
LOCAL_LDLIBS += -landroid
LOCAL_CFLAGS += -O0
LOCAL_CPPFLAGS += -std=c++11
LOCAL_CFLAGS += -DWEBRTC_ANDROID
LOCAL_C_INCLUDES := $(JNI_PATH)
# WebRTC Apm JNI Wrapper inculde C++ Functions and their body
LOCAL_SRC_FILES := $(JNI_PATH)/android_apm_wrapper.cpp
# Here, I basically loaded all the static libraries for different modules i.e. aec, aecm, agc, vad, ns
LOCAL_WHOLE_STATIC_LIBRARIES := libwebrtc_aec \
libwebrtc_aecm \
libwebrtc_agc \
libwebrtc_ns \
libwebrtc_utility \
libwebrtc_vad \
libwebrtc_apm \
libwebrtc_common_audio_vad \
libwebrtc_spl \
libwebrtc_codecs_isac \
libwebrtc_common_audio \
libwebrtc_common_audio_resampler \
libwebrtc_system_wrapper \
libwebrtc_base \
libwebrtc_intelligibility \
libwebrtc_transient \
libwebrtc_beamformer \
libwebrtc_codecs
LOCAL_PRELINK_MODULE := false
include $(BUILD_SHARED_LIBRARY)
Now I can build the shared library via android NDK. To build the shared library, follow these steps;
- Go to the directory of your Apm wrapper such as
path/src/main/jni/android_apm_wrapper.cpp
- Open the command prompt or terminal and build ndk by this command;
ndk-build
Here is the workaround of the ndk-build command:
This command will generates shared library files inside app/src/main/libs and app/src/main/obj directories. The shared library name defined in the make file with LOCAL_MODULE := libwebrtc_apms
Now everything is ready for WebRTC APM Module to pre-process and post-process audio data.
- Push input PCM data into
ProcessCaptureStreamto process in place. - Get the processed PCM data from
ProcessCaptureStreamand send to far-end. - The far end pushed the received data into
ProcessRenderStream.
Now I have integrated WbeRTC APM with my application. I can run it with gradle(in android studio). To run it with gradle I need to manually define the JNI library directory in build.gradle file
android {
--
sourceSets {
main {
jniLibs.srcDir ‘src/main/libs’
jni.srcDirs = []
}
}
--
}
I have published all important source codes inculding an example which mentioned in this article on Android-Audio-Processing-Using-WebRTC. Please refer them if you want.
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