Question

I’m developing an app with native part which uses embedded OpenCV to extract frames from video file. So far I’m getting this error:

.../jni/ocv.c:12: undefined reference to `cvCreateFileCapture'

My Android.mk:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := ocv
LOCAL_SRC_FILES := ocv.c

include $(BUILD_SHARED_LIBRARY)

Application.mk:

APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
APP_ABI := armeabi

ocv.c:

#include <string.h>
#include <jni.h>
#include <stdio.h>
#include <dlfcn.h>
#include <opencv/cv.h>
#include <opencv/highgui.h>

jstring Java_com_ice_salvador_MainActivity_invokeNativeFunction(JNIEnv* env, jobject javaThis) {
    IplImage* currFrame = 0;
    CvCapture* cap = 0;

    cap = cvCaptureFromFile("/mnt/sdcard/vvv.3gp"); //test video

    return (*env)->NewStringUTF(env, "Hello from native code!");
}

I’m using OpenCV-2.4.3-android-sdk, Android NDK r8b, Eclipse Juno, Windows.

IplImage, CvCapture gets resolved and the code compiles if I remove the line with cvCaptureFromFile – so I assume I’m on the right way. I’m new to JNI and OpenCV. Appreciate your help! Thanks.

Answer 1

Not to leave my own question unanswered..

1) I’ve changed Android.mk to include OpenCV.mk from SDK and to include .so lib into the build:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

include c:\dev\OpenCV-2.4.3-android-sdk\sdk\native\jni\OpenCV.mk

LOCAL_MODULE    := ocv
LOCAL_SRC_FILES := ocv.c
LOCAL_LDLIBS += -Lc:\dev\OpenCV-2.4.3-android-sdk\sdk\native\libs\armeabi

include $(BUILD_SHARED_LIBRARY)

#LOCAL_PATH := /home/spatialite/jni
include $(CLEAR_VARS)
LOCAL_MODULE := libopencv_java
LOCAL_SRC_FILES := libopencv_java.so
include $(PREBUILT_SHARED_LIBRARY)

2) Copied libopencv_java.so to jni/ folder.

3) Changed java code to:

static {
  System.loadLibrary("opencv_java");
  System.loadLibrary("ocv");
}

And the error has gone.