How do I use native C libraries in Android Studio

Question

I created a problem some years back based on https://ikaruga2.wordpress.com/2011/06/15/video-live-wallpaper-part-1/. My project was built in the version of Eclipse provided directly by Google at the time and worked fine with a copy of the compiled ffmpeg libraries created with my app name.

Now I'm trying to create a new app based on my old app. As Google no longer supports Eclipse I downloaded Android Studio and imported my project. With a few tweaks, I was able to successfully compile the old version of the project. So I modified the name, copied a new set of ".so" files into app\src\main\jniLibs\armeabi (where I assumed they should go) and tried running the application on my phone again with absolutely no other changes.

The NDK throws no errors. Gradle compiles the file without errors and installs it on my phone. The app appears in my live wallpapers list and I can click it to bring up the preview. But instead of a video appearing I receive and error and logCat reports:

02-26 21:50:31.164  18757-18757/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.ExceptionInInitializerError
        at com.nightscapecreations.anim3free.VideoLiveWallpaper.onSharedPreferenceChanged(VideoLiveWallpaper.java:165)
        at com.nightscapecreations.anim3free.VideoLiveWallpaper.onCreate(VideoLiveWallpaper.java:81)
        at android.app.ActivityThread.handleCreateService(ActivityThread.java:2273)
        at android.app.ActivityThread.access$1600(ActivityThread.java:127)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1212)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4441)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.UnsatisfiedLinkError: Cannot load library: link_image[1936]:   144 could not load needed library '/data/data/com.nightscapecreations.anim1free/lib/libavutil.so' for 'libavcore.so' (load_library[1091]: Library '/data/data/com.nightscapecreations.anim1free/lib/libavutil.so' not found)
        at java.lang.Runtime.loadLibrary(Runtime.java:370)
        at java.lang.System.loadLibrary(System.java:535)
        at com.nightscapecreations.anim3free.NativeCalls.<clinit>(NativeCalls.java:64)
        at com.nightscapecreations.anim3free.VideoLiveWallpaper.onSharedPreferenceChanged(VideoLiveWallpaper.java:165)
        at com.nightscapecreations.anim3free.VideoLiveWallpaper.onCreate(VideoLiveWallpaper.java:81)
        at android.app.ActivityThread.handleCreateService(ActivityThread.java:2273)
        at android.app.ActivityThread.access$1600(ActivityThread.java:127)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1212)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4441)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)

I'm a novice Android/Java/C++ developer and am not sure what this error means, but Google leads me to believe that my new libraries are not being found. In my Eclipse project I had this set of libraries in "libs\armeabi", and another copy of them in a more complicated folder structure at "jni\ffmpeg-android\build\ffmpeg\armeabi\lib". Android Studio appears to have kept everything the same, other than renaming "libs" to "jniLibs", but I'm hitting a brick wall with this error and am unsure how to proceed.

How can I compile this new app with the new name using Android Studio?

In case it helps here is my Android.mk file:

    LOCAL_PATH := $(call my-dir)

    include $(CLEAR_VARS)
    MY_LIB_PATH := ffmpeg-android/build/ffmpeg/armeabi/lib
    LOCAL_MODULE := bambuser-libavcore
    LOCAL_SRC_FILES := $(MY_LIB_PATH)/libavcore.so
    include $(PREBUILT_SHARED_LIBRARY)

    include $(CLEAR_VARS)
    LOCAL_MODULE := bambuser-libavformat
    LOCAL_SRC_FILES := $(MY_LIB_PATH)/libavformat.so
    include $(PREBUILT_SHARED_LIBRARY)

    include $(CLEAR_VARS)
    LOCAL_MODULE := bambuser-libavcodec
    LOCAL_SRC_FILES := $(MY_LIB_PATH)/libavcodec.so
    include $(PREBUILT_SHARED_LIBRARY)

    include $(CLEAR_VARS)
    LOCAL_MODULE := bambuser-libavfilter
    LOCAL_SRC_FILES := $(MY_LIB_PATH)/libavfilter.so
    include $(PREBUILT_SHARED_LIBRARY)

    include $(CLEAR_VARS)
    LOCAL_MODULE := bambuser-libavutil
    LOCAL_SRC_FILES := $(MY_LIB_PATH)/libavutil.so
    include $(PREBUILT_SHARED_LIBRARY)

    include $(CLEAR_VARS)
    LOCAL_MODULE := bambuser-libswscale
    LOCAL_SRC_FILES := $(MY_LIB_PATH)/libswscale.so
    include $(PREBUILT_SHARED_LIBRARY)

    #local_PATH := $(call my-dir)

    include $(CLEAR_VARS)

    LOCAL_CFLAGS := -DANDROID_NDK \
                    -DDISABLE_IMPORTGL

    LOCAL_MODULE    := video
    LOCAL_SRC_FILES := video.c

    LOCAL_C_INCLUDES := \
        $(LOCAL_PATH)/include \
        $(LOCAL_PATH)/ffmpeg-android/ffmpeg \
        $(LOCAL_PATH)/freetype/include/freetype2 \
        $(LOCAL_PATH)/freetype/include \
        $(LOCAL_PATH)/ftgl/src \
        $(LOCAL_PATH)/ftgl
    LOCAL_LDLIBS := -L$(NDK_PLATFORMS_ROOT)/$(TARGET_PLATFORM)/arch-arm/usr/lib -L$(LOCAL_PATH) -L$(LOCAL_PATH)/ffmpeg-android/build/ffmpeg/armeabi/lib/ -lGLESv1_CM -ldl -lavformat -lavcodec -lavfilter -lavutil -lswscale -llog -lz -lm

    include $(BUILD_SHARED_LIBRARY)

And here is my NativeCalls.java:

    package com.nightscapecreations.anim3free;

    public class NativeCalls {
        //ffmpeg
        public static native void initVideo();
        public static native void loadVideo(String fileName); //
        public static native void prepareStorageFrame();
        public static native void getFrame(); //
        public static native void freeConversionStorage();
        public static native void closeVideo();//
        public static native void freeVideo();//
        //opengl
        public static native void initPreOpenGL(); //
        public static native void initOpenGL(); //
        public static native void drawFrame(); //
        public static native void closeOpenGL(); //
        public static native void closePostOpenGL();//
        //wallpaper
        public static native void updateVideoPosition();
        public static native void setSpanVideo(boolean b);
        //getters
        public static native int getVideoHeight();
        public static native int getVideoWidth();
        //setters
        public static native void setWallVideoDimensions(int w,int h);
        public static native void setWallDimensions(int w,int h);
        public static native void setScreenPadding(int w,int h);
        public static native void setVideoMargins(int w,int h);
        public static native void setDrawDimensions(int drawWidth,int drawHeight);
        public static native void setOffsets(int x,int y);
        public static native void setSteps(int xs,int ys);
        public static native void setScreenDimensions(int w, int h);
        public static native void setTextureDimensions(int tx,
                               int ty );
        public static native void setOrientation(boolean b);
        public static native void setPreviewMode(boolean b);
        public static native void setTonality(int t);
        public static native void toggleGetFrame(boolean b);
        //fps
        public static native void setLoopVideo(boolean b);

        static {
        System.loadLibrary("avcore");
        System.loadLibrary("avformat");
        System.loadLibrary("avcodec");
        //System.loadLibrary("avdevice");
        System.loadLibrary("avfilter");
        System.loadLibrary("avutil");
        System.loadLibrary("swscale");
        System.loadLibrary("video");
        }

    }

EDIT

This is the first part of my video.c file:

    #include <GLES/gl.h>
    #include <GLES/glext.h>

    #include <GLES2/gl2.h>
    #include <GLES2/gl2ext.h>

    #include <stdlib.h>
    #include <time.h>

    #include <libavcodec/avcodec.h>
    #include <libavformat/avformat.h>
    #include <libswscale/swscale.h>

    #include <jni.h>  
    #include <string.h>  
    #include <stdio.h>
    #include <android/log.h>

    //#include <FTGL/ftgl.h>

    //ffmpeg video variables
    int      initializedVideo=0;
    int      initializedFrame=0;
    AVFormatContext *pFormatCtx=NULL;
    int             videoStream;
    AVCodecContext  *pCodecCtx=NULL;
    AVCodec         *pCodec=NULL;
    AVFrame         *pFrame=NULL;
    AVPacket        packet;
    int             frameFinished;
    float           aspect_ratio;

    //ffmpeg video conversion variables
    AVFrame         *pFrameConverted=NULL;
    int             numBytes;
    uint8_t         *bufferConverted=NULL;

    //opengl
    int textureFormat=PIX_FMT_RGBA; // PIX_FMT_RGBA   PIX_FMT_RGB24
    int GL_colorFormat=GL_RGBA; // Must match the colorspace specified for textureFormat
    int textureWidth=256;
    int textureHeight=256;
    int nTextureHeight=-256;
    int textureL=0, textureR=0, textureW=0;
    int frameTonality;

    //GLuint textureConverted=0;
    GLuint texturesConverted[2] = { 0,1 };
    GLuint dummyTex = 2;
    static int len=0;


    static const char* BWVertexSrc =
             "attribute vec4 InVertex;\n"
             "attribute vec2 InTexCoord0;\n"
             "attribute vec2 InTexCoord1;\n"
             "uniform mat4 ProjectionModelviewMatrix;\n"
             "varying vec2 TexCoord0;\n"
             "varying vec2 TexCoord1;\n"

             "void main()\n"
             "{\n"
             "  gl_Position = ProjectionModelviewMatrix * InVertex;\n"
             "  TexCoord0 = InTexCoord0;\n"
             "  TexCoord1 = InTexCoord1;\n"
             "}\n";
    static const char* BWFragmentSrc  =

             "#version 110\n"
             "uniform sampler2D Texture0;\n"
             "uniform sampler2D Texture1;\n"

             "varying vec2 TexCoord0;\n"
             "varying vec2 TexCoord1;\n"

             "void main()\n"
             "{\n"
            "   vec3 color = texture2D(m_Texture, texCoord).rgb;\n"
            "   float gray = (color.r + color.g + color.b) / 3.0;\n"
            "   vec3 grayscale = vec3(gray);\n"

            "   gl_FragColor = vec4(grayscale, 1.0);\n"
             "}";
    static GLuint shaderProgram;


    //// Create a pixmap font from a TrueType file.
    //FTGLPixmapFont font("/home/user/Arial.ttf");
    //// Set the font size and render a small text.
    //font.FaceSize(72);
    //font.Render("Hello World!");

    //screen dimensions
    int screenWidth = 50;
    int screenHeight= 50;
    int screenL=0, screenR=0, screenW=0;
    int dPaddingX=0,dPaddingY=0;
    int drawWidth=50,drawHeight=50;

    //wallpaper
    int wallWidth = 50;
    int wallHeight = 50;
    int xOffSet, yOffSet;
    int xStep, yStep;
    jboolean spanVideo = JNI_TRUE;

    //video dimensions
    int wallVideoWidth = 0;
    int wallVideoHeight = 0;
    int marginX, marginY;
    jboolean isScreenPortrait = JNI_TRUE;
    jboolean isPreview = JNI_TRUE;
    jboolean loopVideo = JNI_TRUE;
    jboolean isGetFrame = JNI_TRUE;

    //file
    const char * szFileName;

    #define max( a, b ) ( ((a) > (b)) ? (a) : (b) )
    #define min( a, b ) ( ((a) < (b)) ? (a) : (b) )

    //test variables
    #define RGBA8(r, g, b)  (((r) << (24)) | ((g) << (16)) | ((b) << (8)) | 255)
    int sPixelsInited=JNI_FALSE;
    uint32_t *s_pixels=NULL;

    int s_pixels_size() { 
      return (sizeof(uint32_t) * textureWidth * textureHeight * 5); 
    }

    void render_pixels1(uint32_t *pixels, uint32_t c) {
        int x, y;
        /* fill in a square of 5 x 5 at s_x, s_y */
        for (y = 0; y < textureHeight; y++) {
            for (x = 0; x < textureWidth; x++) {
                int idx = x + y * textureWidth;
                pixels[idx++] = RGBA8(255, 255, 0);
            }
        }
    }

    void render_pixels2(uint32_t *pixels, uint32_t c) {
        int x, y;
        /* fill in a square of 5 x 5 at s_x, s_y */
        for (y = 0; y < textureHeight; y++) {
            for (x = 0; x < textureWidth; x++) {
                int idx = x + y * textureWidth;
                pixels[idx++] = RGBA8(0, 0, 255);
            }
        }
    }

    void Java_com_nightscapecreations_anim3free_NativeCalls_initVideo (JNIEnv * env, jobject this) {
        initializedVideo = 0;
        initializedFrame = 0;
    }

    /* list of things that get loaded: */
    /* buffer */
    /* pFrameConverted */
    /* pFrame */
    /* pCodecCtx */
    /* pFormatCtx */
    void Java_com_nightscapecreations_anim3free_NativeCalls_loadVideo (JNIEnv * env, jobject this, jstring fileName)  {
        jboolean isCopy;
        szFileName = (*env)->GetStringUTFChars(env, fileName, &isCopy);
        //debug
        __android_log_print(ANDROID_LOG_DEBUG, "NDK: ", "NDK:LC: [%s]", szFileName);
        // Register all formats and codecs
        av_register_all();
        // Open video file
        if(av_open_input_file(&pFormatCtx, szFileName, NULL, 0, NULL)!=0) {
        __android_log_print(ANDROID_LOG_DEBUG, "video.c", "NDK: Couldn't open file");
        return;
        }
        __android_log_print(ANDROID_LOG_DEBUG, "video.c", "NDK: Succesfully loaded file");
        // Retrieve stream information */
        if(av_find_stream_info(pFormatCtx)<0) {
        __android_log_print(ANDROID_LOG_DEBUG, "video.c", "NDK: Couldn't find stream information");
        return;
        }
        __android_log_print(ANDROID_LOG_DEBUG, "video.c", "NDK: Found stream info");
        // Find the first video stream
        videoStream=-1;
        int i;
        for(i=0; i<pFormatCtx->nb_streams; i++)
            if(pFormatCtx->streams[i]->codec->codec_type==CODEC_TYPE_VIDEO) {
                videoStream=i;
                break;
            }
        if(videoStream==-1) {
            __android_log_print(ANDROID_LOG_DEBUG, "video.c", "NDK: Didn't find a video stream");
            return;
        }
        __android_log_print(ANDROID_LOG_DEBUG, "video.c", "NDK: Found video stream");
        // Get a pointer to the codec contetx for the video stream
        pCodecCtx=pFormatCtx->streams[videoStream]->codec;
        // Find the decoder for the video stream
        pCodec=avcodec_find_decoder(pCodecCtx->codec_id);
        if(pCodec==NULL) {
            __android_log_print(ANDROID_LOG_DEBUG, "video.c", "NDK: Unsupported codec");
            return;
        }
        // Open codec
        if(avcodec_open(pCodecCtx, pCodec)<0) {
            __android_log_print(ANDROID_LOG_DEBUG, "video.c", "NDK: Could not open codec");
            return;
        }
        // Allocate video frame (decoded pre-conversion frame)
        pFrame=avcodec_alloc_frame();
        // keep track of initialization
        initializedVideo = 1;
        __android_log_print(ANDROID_LOG_DEBUG, "video.c", "NDK: Finished loading video");
    }

    //for this to work, you need to set the scaled video dimensions first
    void Java_com_nightscapecreations_anim3free_NativeCalls_prepareStorageFrame (JNIEnv * env, jobject this)  {
        // Allocate an AVFrame structure
        pFrameConverted=avcodec_alloc_frame();
        // Determine required buffer size and allocate buffer
        numBytes=avpicture_get_size(textureFormat, textureWidth, textureHeight);
        bufferConverted=(uint8_t *)av_malloc(numBytes*sizeof(uint8_t));
        if ( pFrameConverted == NULL || bufferConverted == NULL )
            __android_log_print(ANDROID_LOG_DEBUG, "prepareStorage>>>>", "Out of memory");
        // Assign appropriate parts of buffer to image planes in pFrameRGB
        // Note that pFrameRGB is an AVFrame, but AVFrame is a superset
        // of AVPicture
        avpicture_fill((AVPicture *)pFrameConverted, bufferConverted, textureFormat, textureWidth, textureHeight);
        __android_log_print(ANDROID_LOG_DEBUG, "prepareStorage>>>>", "Created frame");
        __android_log_print(ANDROID_LOG_DEBUG, "prepareStorage>>>>", "texture dimensions: %dx%d", textureWidth, textureHeight);
        initializedFrame = 1;
    }

    jint Java_com_nightscapecreations_anim3free_NativeCalls_getVideoWidth (JNIEnv * env, jobject this)  {
        return pCodecCtx->width;
    }

    jint Java_com_nightscapecreations_anim3free_NativeCalls_getVideoHeight (JNIEnv * env, jobject this)  {
        return pCodecCtx->height;
    }

    void Java_com_nightscapecreations_anim3free_NativeCalls_getFrame (JNIEnv * env, jobject this)  {
        // keep reading packets until we hit the end or find a video packet
        while(av_read_frame(pFormatCtx, &packet)>=0) {
            static struct SwsContext *img_convert_ctx;
            // Is this a packet from the video stream?
            if(packet.stream_index==videoStream) {
                // Decode video frame
                /* __android_log_print(ANDROID_LOG_DEBUG,  */
                /*            "video.c",  */
                /*            "getFrame: Try to decode frame" */
                /*            ); */
                avcodec_decode_video(pCodecCtx, pFrame, &frameFinished, packet.data, packet.size);
                // Did we get a video frame?
                if(frameFinished) {
                    if(img_convert_ctx == NULL) {
                        /* get/set the scaling context */
                        int w = pCodecCtx->width;
                        int h = pCodecCtx->height;
                        img_convert_ctx = sws_getContext(w, h, pCodecCtx->pix_fmt, textureWidth,textureHeight, textureFormat, SWS_FAST_BILINEAR, NULL, NULL, NULL);
                        if(img_convert_ctx == NULL) {
                            return;
                        }
                    }
                    /* if img convert null */
                    /* finally scale the image */
                    /* __android_log_print(ANDROID_LOG_DEBUG,  */
                    /*          "video.c",  */
                    /*          "getFrame: Try to scale the image" */
                    /*          ); */

                    //pFrameConverted = pFrame;
                    sws_scale(img_convert_ctx, pFrame->data, pFrame->linesize, 0, pCodecCtx->height, pFrameConverted->data, pFrameConverted->linesize);
                    //av_picture_crop(pFrameConverted->data, pFrame->data, 1, pCodecCtx->height, pCodecCtx->width);
                    //av_picture_crop();
                    //avfilter_vf_crop();

                    /* do something with pFrameConverted */
                    /* ... see drawFrame() */
                    /* We found a video frame, did something with it, now free up
                       packet and return */
                    av_free_packet(&packet);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrame.age: %d", pFrame->age);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrame.buffer_hints: %d", pFrame->buffer_hints);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrame.display_picture_number: %d", pFrame->display_picture_number);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrame.hwaccel_picture_private: %d", pFrame->hwaccel_picture_private);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrame.key_frame: %d", pFrame->key_frame);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrame.palette_has_changed: %d", pFrame->palette_has_changed);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrame.pict_type: %d", pFrame->pict_type);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrame.qscale_type: %d", pFrame->qscale_type);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrameConverted.age: %d", pFrameConverted->age);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrameConverted.buffer_hints: %d", pFrameConverted->buffer_hints);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrameConverted.display_picture_number: %d", pFrameConverted->display_picture_number);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrameConverted.hwaccel_picture_private: %d", pFrameConverted->hwaccel_picture_private);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrameConverted.key_frame: %d", pFrameConverted->key_frame);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrameConverted.palette_has_changed: %d", pFrameConverted->palette_has_changed);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrameConverted.pict_type: %d", pFrameConverted->pict_type);
    //              __android_log_print(ANDROID_LOG_INFO, "Droid Debug", "pFrameConverted.qscale_type: %d", pFrameConverted->qscale_type);
                    return;
                } /* if frame finished */
            } /* if packet video stream */
            // Free the packet that was allocated by av_read_frame
            av_free_packet(&packet);
        } /* while */
        //reload video when you get to the end
        av_seek_frame(pFormatCtx,videoStream,0,AVSEEK_FLAG_ANY);
    }

    void Java_com_nightscapecreations_anim3free_NativeCalls_setLoopVideo (JNIEnv * env, jobject this, jboolean b) {
        loopVideo = b;
    }

    void Java_com_nightscapecreations_anim3free_NativeCalls_closeVideo (JNIEnv * env, jobject this) {
        if ( initializedFrame == 1 ) {
            // Free the converted image
            av_free(bufferConverted);
            av_free(pFrameConverted);
            initializedFrame = 0;
            __android_log_print(ANDROID_LOG_DEBUG, "closeVideo>>>>", "Freed converted image");
        }
        if ( initializedVideo == 1 ) {
            /* // Free the YUV frame */
            av_free(pFrame);
            /* // Close the codec */
            avcodec_close(pCodecCtx);
            // Close the video file
            av_close_input_file(pFormatCtx);
            initializedVideo = 0;
            __android_log_print(ANDROID_LOG_DEBUG, "closeVideo>>>>", "Freed video structures");
        }
    }

    void Java_com_nightscapecreations_anim3free_NativeCalls_freeVideo (JNIEnv * env, jobject this) {
        if ( initializedVideo == 1 ) {
            /* // Free the YUV frame */
            av_free(pFrame);
            /* // Close the codec */
            avcodec_close(pCodecCtx);
            // Close the video file
            av_close_input_file(pFormatCtx);
            __android_log_print(ANDROID_LOG_DEBUG, "closeVideo>>>>", "Freed video structures");
            initializedVideo = 0;
        }
    }

    void Java_com_nightscapecreations_anim3free_NativeCalls_freeConversionStorage (JNIEnv * env, jobject this) {
        if ( initializedFrame == 1 ) {
            // Free the converted image
            av_free(bufferConverted);
            av_freep(pFrameConverted);
            initializedFrame = 0;
        }
    }

    /*--- END OF VIDEO ----*/

    /* disable these capabilities. */
    static GLuint s_disable_options[] = {
        GL_FOG,
        GL_LIGHTING,
        GL_CULL_FACE,
        GL_ALPHA_TEST,
        GL_BLEND,
        GL_COLOR_LOGIC_OP,
        GL_DITHER,
        GL_STENCIL_TEST,
        GL_DEPTH_TEST,
        GL_COLOR_MATERIAL,
        0
    };

    // For stuff that opengl needs to work with,
    // like the bitmap containing the texture
    void Java_com_nightscapecreations_anim3free_NativeCalls_initPreOpenGL (JNIEnv * env, jobject this)  {

    }
    ...

Solution

if you only want to reuse your former lib and not compiling anything with the NDK, you can simply drop all your .so files inside jniLibs/<abi>.

Else, as your ndk build depend on prebuilts, you can't configure it properly to work directly with gradle configuration (ndk{}). Anyway, as the ndk support is deprecated for now, the most clean way to make it work is to make gradle call ndk-build and use your existing Makefiles:

import org.apache.tools.ant.taskdefs.condition.Os

...

android {  
  ...
  sourceSets.main {
        jniLibs.srcDir 'src/main/libs' //set .so files location to libs instead of jniLibs
        jni.srcDirs = [] //disable automatic ndk-build call
    }

    // add a task that calls regular ndk-build(.cmd) script from app directory
    task ndkBuild(type: Exec) {
        if (Os.isFamily(Os.FAMILY_WINDOWS)) {
            commandLine 'ndk-build.cmd', '-C', file('src/main').absolutePath
        } else {
            commandLine 'ndk-build', '-C', file('src/main').absolutePath
        }
    }

    // add this task as a dependency of Java compilation
    tasks.withType(JavaCompile) {
        compileTask -> compileTask.dependsOn ndkBuild
    }
}