Example. Works fine without main methods

app/build.gradle

@@ -46,5 +46,4 @@ android {
 
 dependencies {
     implementation fileTree(dir: "libs", include: ["*.jar"])
-    implementation 'androidx.appcompat:appcompat:1.2.0'
 }

app/src/main/AndroidManifest.xml

@@ -1,11 +1,2 @@
 <?xml version="1.0" encoding="utf-8"?>
-<manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    package="linc.com.amplituda">
-    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
-    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
-    <application
-        android:allowBackup="true"
-        android:label="@string/app_name"
-        android:supportsRtl="true"
-        android:extractNativeLibs="false"/>
-</manifest>
+<manifest package="linc.com.amplituda"/>

app/src/main/cpp/native-lib.cpp

@@ -1,10 +1,20 @@
 #include <jni.h>
+#include <string>
 
 extern "C" {
 #include "libavcodec/avcodec.h"
 #include "libavformat/avformat.h"
 }
 
+std::string ConvertJString(JNIEnv* env, jstring str){
+    if ( !str ) std::string();
+    const jsize len = env->GetStringUTFLength(str);
+    const char* strChars = env->GetStringUTFChars(str, (jboolean *)0);
+    std::string Result(strChars, len);
+    env->ReleaseStringUTFChars(str, strChars);
+    return Result;
+}
+
 float getSample(const AVCodecContext* codecCtx, uint8_t* buffer, int sampleIndex) {
     int64_t val = 0;
     float ret = 0;
@@ -15,19 +25,12 @@ float getSample(const AVCodecContext* codecCtx, uint8_t* buffer, int sampleIndex
             val = (reinterpret_cast<uint8_t*>(buffer))[sampleIndex];
             val -= 127;
             break;
-
-        case 2:
-            val = (reinterpret_cast<uint16_t*>(buffer))[sampleIndex];
+        case 2: val = (reinterpret_cast<uint16_t*>(buffer))[sampleIndex];
             break;
-
-        case 4:
-            val = (reinterpret_cast<uint32_t*>(buffer))[sampleIndex];
+        case 4: val = (reinterpret_cast<uint32_t*>(buffer))[sampleIndex];
             break;
-
-        case 8:
-            val = (reinterpret_cast<uint64_t*>(buffer))[sampleIndex];
+        case 8: val = (reinterpret_cast<uint64_t*>(buffer))[sampleIndex];
             break;
-
         default:
             return 0;
     }
@@ -43,21 +46,17 @@ float getSample(const AVCodecContext* codecCtx, uint8_t* buffer, int sampleIndex
             // integer => Scale to [-1, 1] and convert to float.
             ret = val / (static_cast<float>(((1 << (sampleSize*8-1))-1)));
             break;
-
         case AV_SAMPLE_FMT_FLT:
         case AV_SAMPLE_FMT_FLTP:
             // float => reinterpret
             ret = *reinterpret_cast<float*>(&val);
             break;
-
         case AV_SAMPLE_FMT_DBL:
         case AV_SAMPLE_FMT_DBLP:
             // double => reinterpret and then static cast down
             ret = static_cast<float>(*reinterpret_cast<double*>(&val));
             break;
-
         default:
-//            fprintf(stderr, "Invalid sample format %s.\n", av_get_sample_fmt_name(codecCtx->sample_fmt));
             return 0;
     }
 
@@ -69,93 +68,61 @@ extern "C" JNIEXPORT jstring JNICALL
 
 Java_linc_com_amplituda_Amplituda_stringFromJNI(
         JNIEnv* env,
-        jobject) {
-    // You can change the filename for any other filename/supported format
-//    const char *filename = "../my file.ogg";
+        jobject,
+        jstring audio_path
+        ) {
 
-//    std::string resultFrame = "";
+    std::string filename = ConvertJString( env, audio_path );
+    std::string resultFrame;
 
-    // SUPPORTED AUDIO FORMATS
-    // [mp3, opus, oga, ogg, m4a, mp4] / 1h audio processing = 30sec
-
-//    const char *filename = "/storage/emulated/0/viber/kygo.mp3";
-//    const char *filename = "/storage/emulated/0/viber/ex.wav";
-    const char *filename = "/storage/emulated/0/Android/data/org.thunderdog.challegram/files/music/f_voip_dur.opus";
-//    const char *filename = "/storage/emulated/0/Android/data/org.thunderdog.challegram/files/music/Голос 0017325996153317080688.m4a";
-//    const char *filename = "/storage/emulated/0/Android/data/org.thunderdog.challegram/files/video_notes/5406735884265457666.mp4";
-//    const char *filename = "/storage/emulated/0/Android/data/org.thunderdog.challegram/files/voice/5382102159468791418.oga";
-//    const char *filename = "/storage/emulated/0/Android/data/org.thunderdog.challegram/files/music/DiscDj_Rec_2020-06-21_18-38-44.mp3";
-
-    // Initialize FFmpeg
     av_register_all();
 
-//    AVFrame* frame = avcodec_alloc_frame();
     AVFrame* frame = av_frame_alloc();
 
-    if (!frame)
-    {
-//        std::cout << "Error allocating the frame.  Let's try again shall we?\n";
-        return env->NewStringUTF("666");  // fail at start: 66 = number of the beast
+    if (!frame){
+        return env->NewStringUTF("Error allocating the frame! Amplituda:exception:600");
     }
 
-    // you can change the file name to whatever yo need:)
     AVFormatContext* formatContext = NULL;
-    if (avformat_open_input(&formatContext, filename, NULL, NULL) != 0)
-    {
+    if (avformat_open_input(&formatContext, filename.data(), NULL, NULL) != 0) {
         av_free(frame);
-//        std::cout << "Error opening file " << filename<< "\n";
-        return env->NewStringUTF("800"); // cant open file.  800 = Boo!
+        return env->NewStringUTF("Error opening file! Amplituda:exception:800");
     }
 
-    if (avformat_find_stream_info(formatContext, NULL) < 0)
-    {
+    if (avformat_find_stream_info(formatContext, NULL) < 0){
         av_free(frame);
         avformat_close_input(&formatContext);
-//        std::cout << "Error finding the stream information.\nCheck your paths/connections and the details you supplied!\n";
-        return env->NewStringUTF("57005"); // stream info error.  0xDEAD in hex is 57005 in decimal
+        return env->NewStringUTF("Error finding the stream information! Amplituda:exception:57005");
     }
 
-    // Find the audio stream
     AVCodec* cdc = nullptr;
     int streamIndex = av_find_best_stream(formatContext, AVMEDIA_TYPE_AUDIO, -1, -1, &cdc, 0);
-    if (streamIndex < 0)
-    {
+    if (streamIndex < 0){
         av_free(frame);
         avformat_close_input(&formatContext);
-//        std::cout << "Could not find any audio stream in the file.  Come on! I need data!\n";
-        return env->NewStringUTF("165"); // no(0) (a)udio s(5)tream:  0A5 in hex = 165 in decimal
+        return env->NewStringUTF("Could not find any audio stream in the file! Amplituda:exception:165");
     }
 
     AVStream* audioStream = formatContext->streams[streamIndex];
     AVCodecContext* codecContext = audioStream->codec;
     codecContext->codec = cdc;
 
-    if (avcodec_open2(codecContext, codecContext->codec, NULL) != 0)
-    {
+    if (avcodec_open2(codecContext, codecContext->codec, NULL) != 0){
         av_free(frame);
         avformat_close_input(&formatContext);
-//        std::cout << "Couldn't open the context with the decoder.  I can decode but I need to have something to decode.\nAs I couldn't find anything I have surmised the decoded output is 0!\n (Well can't have you thinking I am doing nothing can we?\n";
-        return env->NewStringUTF("1057"); // cant find/open context 1057 = lost
+        return env->NewStringUTF("Couldn't open the context with the decoder! (can't find or open context) Amplituda:exception:1057");
     }
 
-//    std::cout << "This stream has " << codecContext->channels << " channels with a sample rate of " << codecContext->sample_rate << "Hz\n";
-//    std::cout << "The data presented in format: " << av_get_sample_fmt_name(codecContext->sample_fmt) << std::endl;
-
     AVPacket readingPacket;
     av_init_packet(&readingPacket);
 
-    // Read the packets in a loop
     while (av_read_frame(formatContext, &readingPacket) == 0)
     {
         if (readingPacket.stream_index == audioStream->index)
         {
             AVPacket decodingPacket = readingPacket;
-            // Audio packets can have multiple audio frames in a single packet
             while (decodingPacket.size > 0)
             {
-                // Try to decode the packet into a frame(s)
-                // Some frames rely on multiple packets, so we have to make sure the frame is finished
-                // before utilising it
                 int gotFrame = 0;
                 int result = avcodec_decode_audio4(codecContext, frame, &gotFrame, &decodingPacket);
 
@@ -165,23 +132,22 @@ Java_linc_com_amplituda_Amplituda_stringFromJNI(
                     decodingPacket.data += result;
 
                     float sum = 0;
-//                    for(int s = 0; s < frame->nb_samples; ++s) {
                     for(int s = 0; s < 4; ++s) {
                         for(int c = 0; c < codecContext->channels; ++c) {
                             float sample = getSample(codecContext, frame->extended_data[c], s);
                             if(sample < 0)
                                 sum += -sample;
                             else
                                 sum += sample;
-//                            __android_log_print(ANDROID_LOG_VERBOSE, "NDK_NDK_NDK", "First loop = %f", sample);
                         }
                     }
-                    float average_point = (sum * 2) / 4;
+//                    float average_point = (sum * 2) / 4;
 
-                    int ampl_av = pow(((int)(average_point * 100)), 0.5);
+//                    int amplitude = pow(((int)(average_point * 100)), 0.5);
+                    int amplitude = pow(((int)(((sum * 2) / 4) * 100)), 0.5);
 
-//                    resultFrame.append(std::to_string(  ampl_av ));
-//                    resultFrame.append("\n");
+                    resultFrame.append(std::to_string(  amplitude ));
+                    resultFrame.append("\n");
                 }
                 else
                 {
@@ -191,15 +157,11 @@ Java_linc_com_amplituda_Amplituda_stringFromJNI(
             }
         }
 
-        // You MUST call av_free_packet() after each call to av_read_frame()
-        // or you will leak so much memory on a large file you will need a memory-plumber!
         av_free_packet(&readingPacket);
     }
 
-    // Clean up! (unless you have a quantum memory machine with infinite RAM....)
     av_free(frame);
     avcodec_close(codecContext);
     avformat_close_input(&formatContext);
-//    return env->NewStringUTF(resultFrame.data()); // success!!!!!!!!
-    return env->NewStringUTF("0"); // success!!!!!!!!
+    return env->NewStringUTF(resultFrame.data());
 }

app/src/main/java/linc/com/amplituda/Amplituda.java

@@ -1,18 +1,45 @@
 package linc.com.amplituda;
 
+import android.content.Context;
+
 public class Amplituda {
 
     static {
         System.loadLibrary("native-lib");
     }
 
-    public void init() {
-        System.out.println("AMPLITUDE ===================== " + stringFromJNI());
+    public void init(SuccessCallback successCallback) {
+//        System.out.println("AMPLITUDE ===================== " + stringFromJNI());
+        successCallback.onSuccess(stringFromJNI("/storage/emulated/0/viber/kygo.mp3"));
+        //    const char *filename = "/storage/emulated/0/viber/kygo.mp3";
+//    const char *filename = "/storage/emulated/0/viber/ex.wav";
+//    const char *filename = "/storage/emulated/0/Android/data/org.thunderdog.challegram/files/music/f_voip_dur.opus";
+//    const char *filename = "/storage/emulated/0/Android/data/org.thunderdog.challegram/files/music/Голос 0017325996153317080688.m4a";
+//    const char *filename = "/storage/emulated/0/Android/data/org.thunderdog.challegram/files/video_notes/5406735884265457666.mp4";
+//    const char *filename = "/storage/emulated/0/Android/data/org.thunderdog.challegram/files/voice/5382102159468791418.oga";
+//    const char *filename = "/storage/emulated/0/Android/data/org.thunderdog.challegram/files/music/DiscDj_Rec_2020-06-21_18-38-44.mp3";
+        // SUPPORTED AUDIO FORMATS
+        // [mp3, opus, oga, ogg, m4a, mp4] / 1h audio processing = 30sec
+
     }
 
+    public Amplituda withContext(Context context) {
+        return this;
+    }
+    public Amplituda fromFile() {
+        return this;
+    }
+    public Amplituda fromPath() {
+        return this;
+    }
     /**
      * A native method that is implemented by the 'native-lib' native library,
      * which is packaged with this application.
      */
-    native String stringFromJNI();
+    native String stringFromJNI(String pathToAudio);
+
+    public interface SuccessCallback {
+        void onSuccess(String log);
+    }
+
 }

example/.gitignore

@@ -0,0 +1 @@
+/build

example/build.gradle

@@ -0,0 +1,34 @@
+apply plugin: 'com.android.application'
+
+android {
+    compileSdkVersion 29
+    buildToolsVersion "29.0.3"
+    ndkVersion "21.3.6528147"
+
+    defaultConfig {
+        applicationId "linc.com.example"
+        minSdkVersion 21
+        targetSdkVersion 29
+        versionCode 1
+        versionName "1.0"
+
+        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
+    }
+
+    buildTypes {
+        release {
+            minifyEnabled false
+            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
+        }
+    }
+    compileOptions {
+        sourceCompatibility JavaVersion.VERSION_1_8
+        targetCompatibility JavaVersion.VERSION_1_8
+    }
+}
+
+dependencies {
+    implementation fileTree(dir: "libs", include: ["*.jar"])
+    implementation 'androidx.appcompat:appcompat:1.2.0'
+    implementation project(":app")
+}

example/proguard-rules.pro

@@ -0,0 +1,21 @@
+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

example/src/androidTest/java/linc/com/example/ExampleInstrumentedTest.java

@@ -0,0 +1,26 @@
+package linc.com.example;
+
+import android.content.Context;
+
+import androidx.test.platform.app.InstrumentationRegistry;
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import static org.junit.Assert.*;
+
+/**
+ * Instrumented test, which will execute on an Android device.
+ *
+ * @see <a href="http://d.android.com/tools/testing">Testing documentation</a>
+ */
+@RunWith(AndroidJUnit4.class)
+public class ExampleInstrumentedTest {
+    @Test
+    public void useAppContext() {
+        // Context of the app under test.
+        Context appContext = InstrumentationRegistry.getInstrumentation().getTargetContext();
+        assertEquals("linc.com.example", appContext.getPackageName());
+    }
+}