因此，我尝试制作一个Android应用程序，该应用程序将通过OpenCV通过JNI和NDK逐帧打开视频文件，检测每个帧中的人脸并显示它们(最终目标是使算法更准确，以更好地适应糟糕的移动设备处理)。
我尝试的第一种方法是MediaMetadataRetriever，没有结果，它只是返回null。
第二种方法是FFMpegMediaMetadataRetriever，它可以按预期运行，但是非常慢(最高2fps；太慢)，部分原因是必须将FFMpegMMR的位图转换为Mat，然后检测并绘制，然后再转换回位图，这非常我的穴居人甚至尝试。
我当前正在使用的第三个方法是VideoCapturegrab()和retrieve()。我为本机代码做了一个包装，主要是通过从OpenCV示例中复制facedtector来完成的。我还尝试了read()，它应该将两者结合起来，但是也会导致致命的信号11(在某些被遗忘的OpenCV或Android平台上出现分段错误)。
这是应用程序获取绝对文件路径的方式(请注意，它确实适用于FFMpegMMR):
//The file name, file path and filerawresource are used in getting the path of the video file on device's disk
String videoFileName="samplemp4";
String videoFileType=".mp4";
int videoFileRawResourceId=R.raw.samplemp4;
public String getVideoFilePath()
{
InputStream is = getResources().openRawResource(videoFileRawResourceId);
File sampleDir = getDir(videoFileName, Context.MODE_PRIVATE);
File sampleFile= new File(sampleDir, videoFileName+videoFileType);
try {
FileOutputStream os = new FileOutputStream(sampleFile);
byte[] buffer = new byte[4096];
int bytesRead;
while ((bytesRead = is.read(buffer)) != -1) {
os.write(buffer, 0, bytesRead);
}
is.close();
os.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
File videoDir = getDir(videoFileName, Context.MODE_PRIVATE);
File videoFile = new File(videoDir, videoFileName+videoFileType);
return videoFile.getAbsolutePath();
}
这是调用本机方法的java包装器并使用结果的地方:
class AsyncPlay extends AsyncTask<String, Mat, Bitmap>
{
@Override
protected Bitmap doInBackground(String... params) {
//for(;play;)
{
if(play)
{
if(currentTime==0)
{
test=new Test();
test.startTime.setToNow();
test.type="Video";
frameGrabber.open(videoFilePath);
}
//publishProgress(retriever.getFrameAtTime(currentTime*1000+111,
// FFmpegMediaMetadataRetriever.OPTION_CLOSEST));
Mat tmp=new Mat();
//frameGrabber.read(tmp);
frameGrabber.grab();
frameGrabber.retrieve(tmp);
publishProgress(tmp);
currentTime+=111;
if(currentTime*1000>=duration*1000)
{
currentTime=0;
test.endTime.setToNow();
tester.publishResult(test);
frameGrabber.release();
}
}
try
{
Thread.sleep(111);
} catch (InterruptedException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return null;
}
@Override
protected void onProgressUpdate(Mat... values) {
//face detection logic goes here
//Bitmap bmp=values[0];
//Mat rgbMat = new Mat();
//Utils.bitmapToMat(bmp, rgbMat);
DetectionResult detectionResult = openCVFaceDetector.detectFromImage(values[0], Imgproc.COLOR_RGB2GRAY);//Detecting with a native detector from OpenCV
test.addDetection(detectionResult.detection);
imageViewOriginal.setImageBitmap(detectionResult.detectedImage);
super.onProgressUpdate(values);
}
};`
其中FrameGrabber frameGrabber是本机的Java包装程序，并且在调用retrieve()或read()时会发送信号，请注意，构造函数，open()和grab()都可以工作(或者至少不会使应用程序崩溃) )。
这是包装器(我正确地传递了VideoCapture对象，我知道这是致命信号的原因之一):
import org.opencv.core.Mat;
public class FrameGrabber
{
private long mNativeObj = 0;
private static native long nativeCreateObject(String fileName);
private static native void nativeDestroyObject(long thiz);
private static native boolean nativeOpen(long thiz, String fileName);
private static native boolean nativeGrab(long thiz);
private static native boolean nativeRetrieve(long thiz, Mat imageMat);
private static native boolean nativeRead(long thiz, Mat imageMat);
private static native void nativeRelease(long thiz);
public FrameGrabber(String fileName) {
mNativeObj = nativeCreateObject(fileName);
}
public void destroy() {
nativeDestroyObject(mNativeObj);
mNativeObj = 0;
}
public boolean open(String fileName)
{
return nativeOpen(mNativeObj, fileName);
}
public boolean grab()
{
return nativeGrab(mNativeObj);
}
public boolean retrieve(Mat imageMat)
{
return nativeRetrieve(mNativeObj, imageMat);
}
public boolean read(Mat imageMat)
{
return nativeRead(mNativeObj, imageMat);
}
public void release()
{
nativeRelease(mNativeObj);
}
}
这是它的本机部分(导致错误的确切行是
result = ((VideoCapture*)thiz)->retrieve((*((Mat*)imageMat)));，它在nativeRetrieve()方法中#include <string>
#include <vector>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <FrameGrabber_jni.h>
#include <android/log.h>
#define LOG_TAG "FrameGrabber"
#define LOGD(...) ((void)__android_log_print(ANDROID_LOG_DEBUG, LOG_TAG, __VA_ARGS__))
using namespace std;
using namespace cv;
inline void jStringToString(JNIEnv * jenv, jstring jString, string stdName)
{
LOGD("Java_boris_springar_diplomska_FrameGrabber_jStringToString enter");
LOGD("grabber is Making jnamestr");//this is buggy as hell, the line serves as a debug tool
const char* jnamestr = jenv->GetStringUTFChars(jString, NULL);
string stdNameTmp(jnamestr);
stdName=stdNameTmp;
LOGD("grabber is releasing jnamestr");
jenv->ReleaseStringUTFChars(jString, jnamestr);
}
/*
* CONSTRUCTOR AND DESTRUCTOR
*/
JNIEXPORT jlong JNICALL Java_boris_springar_diplomska_FrameGrabber_nativeCreateObject
(JNIEnv * jenv, jclass, jstring jFileName)
{
LOGD("Java_boris_springar_diplomska_FrameGrabber_nativeCreateObject enter");
string stdFileName;
jStringToString(jenv, jFileName,stdFileName);
jlong result = 0;
try
{
result = (jlong)new VideoCapture(stdFileName);
}
catch(cv::Exception& e)
{
LOGD("nativeCreateObject caught cv::Exception: %s", e.what());
jclass je = jenv->FindClass("org/opencv/core/CvException");
if(!je)
je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, e.what());
}
catch (...)
{
LOGD("nativeCreateObject caught unknown exception");
jclass je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, "Unknown exception in JNI code of FrameGrabber.nativeCreateObject()");
return 0;
}
LOGD("Java_boris_springar_diplomska_FrameGrabber_nativeCreateObject exit");
return result;
}
//should work
JNIEXPORT void JNICALL Java_boris_springar_diplomska_FrameGrabber_nativeDestroyObject
(JNIEnv * jenv, jclass, jlong thiz)
{
LOGD("Java_boris_springar_diplomska_FrameGrabber_nativeDestroyObject enter");
try
{
if(thiz != 0)
{
delete (VideoCapture*)thiz;
}
}
catch(cv::Exception& e)
{
LOGD("nativeestroyObject caught cv::Exception: %s", e.what());
jclass je = jenv->FindClass("org/opencv/core/CvException");
if(!je)
je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, e.what());
}
catch (...)
{
LOGD("nativeDestroyObject caught unknown exception");
jclass je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, "Unknown exception in JNI code of FrameGrabber.nativeDestroyObject()");
}
LOGD("Java_boris_springar_diplomska_FrameGrabber_nativeDestroyObject exit");
}
/*
* CORE METHODS
*/
//Open function opens the filename for playing
JNIEXPORT jboolean JNICALL Java_boris_springar_diplomska_FrameGrabber_nativeOpen
(JNIEnv * jenv, jclass,jlong thiz,jstring jFileName)
{
LOGD("Java_boris_springar_diplomska_FrameGrabber_open enter");
string stdFileName;
jStringToString(jenv, jFileName,stdFileName);
jboolean result = false;
try
{
result = ((VideoCapture*)thiz)->open(stdFileName);
}
catch(cv::Exception& e)
{
LOGD("frame grabber open exception caught cv::Exception: %s", e.what());
jclass je = jenv->FindClass("org/opencv/core/CvException");
if(!je)
je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, e.what());
}
catch (...)
{
LOGD("frame grabber open caught unknown exception");
jclass je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, "Unknown exception in JNI code of FrameGrabber.open()");
return 0;
}
LOGD("Java_boris_springar_diplomska_FrameGrabber_open exit");
return result;
}
//grab grabs the next frame from file or camera
JNIEXPORT jboolean JNICALL Java_boris_springar_diplomska_FrameGrabber_nativeGrab
(JNIEnv * jenv, jclass,jlong thiz)
{
LOGD("Java_boris_springar_diplomska_FrameGrabber_grab enter");
jboolean result = false;
try
{
result = ((VideoCapture*)thiz)->grab();
}
catch(cv::Exception& e)
{
LOGD("frame grabber grab exception caught cv::Exception: %s", e.what());
jclass je = jenv->FindClass("org/opencv/core/CvException");
if(!je)
je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, e.what());
}
catch (...)
{
LOGD("frame grabber grab caught unknown exception");
jclass je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, "Unknown exception in JNI code of FrameGrabber.grab()");
return 0;
}
LOGD("Java_boris_springar_diplomska_FrameGrabber_grab exit");
return result;
}
//retrieve retrieves the next frame and writes it to the image matrix
JNIEXPORT jboolean JNICALL Java_boris_springar_diplomska_FrameGrabber_nativeRetrieve
(JNIEnv * jenv, jclass,jlong thiz, jlong imageMat)
{
LOGD("Java_boris_springar_diplomska_FrameGrabber_retrieve enter");
jboolean result = false;
try
{
LOGD("grabber trying to retrieve");
result = ((VideoCapture*)thiz)->retrieve((*((Mat*)imageMat)));//should write the current frame to the image matrix
}
catch(cv::Exception& e)
{
LOGD("frame grabber retrieve exception caught cv::Exception: %s", e.what());
jclass je = jenv->FindClass("org/opencv/core/CvException");
if(!je)
je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, e.what());
}
catch (...)
{
LOGD("frame grabber retrieve caught unknown exception");
jclass je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, "Unknown exception in JNI code of FrameGrabber.retrieve(fileName)");
return 0;
}
LOGD("Java_boris_springar_diplomska_FrameGrabber_retrieve exit");
return result;
}
//read combines grab and retrieve and writes the stuff to the image matrix
JNIEXPORT jboolean JNICALL Java_boris_springar_diplomska_FrameGrabber_nativeRead
(JNIEnv * jenv, jclass,jlong thiz, jlong imageMat)
{
LOGD("Java_boris_springar_diplomska_FrameGrabber_read enter");
LOGD("grabber setting result to false");
jboolean result = false;
try
{
LOGD("grabber trying to read capture");
result = ((VideoCapture*)thiz)->read((*((Mat*)imageMat)));//should write the current frame to the image matrix
}
catch(cv::Exception& e)
{
LOGD("frame grabber read exception caught cv::Exception: %s", e.what());
jclass je = jenv->FindClass("org/opencv/core/CvException");
if(!je)
je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, e.what());
}
catch (...)
{
LOGD("frame grabber read caught unknown exception");
jclass je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, "Unknown exception in JNI code of FrameGrabber.open(fileName)");
return 0;
}
LOGD("Java_boris_springar_diplomska_FrameGrabber_read exit");
return result;
}
//Release releases the resource it's using, I hope
JNIEXPORT void JNICALL Java_boris_springar_diplomska_FrameGrabber_nativeRelease
(JNIEnv * jenv, jclass,jlong thiz)
{
LOGD("Java_boris_springar_diplomska_FrameGrabber_release enter");
jboolean result = false;
try
{
((VideoCapture*)thiz)->release();//should release
}
catch(cv::Exception& e)
{
LOGD("frame grabber read exception caught cv::Exception: %s", e.what());
jclass je = jenv->FindClass("org/opencv/core/CvException");
if(!je)
je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, e.what());
}
catch (...)
{
LOGD("frame grabber release caught unknown exception");
jclass je = jenv->FindClass("java/lang/Exception");
jenv->ThrowNew(je, "Unknown exception in JNI code of FrameGrabber.open(fileName)");
}
LOGD("Java_boris_springar_diplomska_FrameGrabber_release exit");
}
还有LogCat输出:
07-22 17:36:24.886: D/FrameGrabber(15359): Java_boris_springar_diplomska_FrameGrabber_nativeCreateObject enter
07-22 17:36:24.886: D/FrameGrabber(15359): Java_boris_springar_diplomska_FrameGrabber_jStringToString enter
07-22 17:36:24.886: D/FrameGrabber(15359): grabber is Making jnamestr
07-22 17:36:24.886: D/FrameGrabber(15359): grabber is releasing jnamestr
07-22 17:36:24.886: D/FrameGrabber(15359): Java_boris_springar_diplomska_FrameGrabber_nativeCreateObject exit
07-22 17:36:24.936: I/dalvikvm(15359): threadid=3: reacting to signal 3
07-22 17:36:24.936: I/dalvikvm(15359): Wrote stack traces to '/data/anr/traces.txt'
07-22 17:36:24.946: D/libEGL(15359): loaded /system/lib/egl/libEGL_mali.so
07-22 17:36:24.956: D/libEGL(15359): loaded /system/lib/egl/libGLESv1_CM_mali.so
07-22 17:36:24.976: D/libEGL(15359): loaded /system/lib/egl/libGLESv2_mali.so
07-22 17:36:25.006: D/OpenGLRenderer(15359): Enabling debug mode 0
07-22 17:36:27.336: D/FrameGrabber(15359): Java_boris_springar_diplomska_FrameGrabber_open enter
07-22 17:36:27.336: D/FrameGrabber(15359): Java_boris_springar_diplomska_FrameGrabber_jStringToString enter
07-22 17:36:27.336: D/FrameGrabber(15359): grabber is Making jnamestr
07-22 17:36:27.336: D/FrameGrabber(15359): grabber is releasing jnamestr
07-22 17:36:27.336: D/FrameGrabber(15359): Java_boris_springar_diplomska_FrameGrabber_open exit
07-22 17:36:27.336: D/FrameGrabber(15359): Java_boris_springar_diplomska_FrameGrabber_grab enter
07-22 17:36:27.336: D/FrameGrabber(15359): Java_boris_springar_diplomska_FrameGrabber_grab exit
07-22 17:36:27.336: D/FrameGrabber(15359): Java_boris_springar_diplomska_FrameGrabber_retrieve enter
07-22 17:36:27.336: D/FrameGrabber(15359): grabber trying to retrieve
07-22 17:36:27.336: A/libc(15359): Fatal signal 11 (SIGSEGV) at 0x1d400019 (code=1)
调试此代码的问题在于，它是Eclipse中的JNI，我什至不知道如何在Eclipse中调试c++，这就是为什么我使用日志消息来查找代码中的错误。那些方法极大地帮助了我，因为open()和grab()无法正常工作，我发现并消除了一个错误，在那里我忘了将方法传递给这些错误。使用retrieve()的问题在于，我一生无法找到它的来源。 highgui.hpp中有部分定义，但没有实现，可以在其中放置日志消息以帮助调试。
可能的解决方案是:
因此，如果有人可以告诉我在哪里可以找到retrieve()和read()的实现，我将不胜感激。或者，如果我错过了一些明显而愚蠢的事情(我希望)。
同时，我将尝试找到一种在Eclipse中调试c++的方法，并尝试其他格式？
最佳答案
终于找到了它，遵循Aleksander的建议，我设法找到了从Java传递到JNI的对象的类型不匹配。
事实证明，错误出在声明了本机方法的Java部分中。除了传递Mat之外，我还必须传递Mat.getNativeObjAddr()，这很长。
所以代替
private static native boolean nativeRetrieve(long thiz, Mat imageMat);
private static native boolean nativeRead(long thiz, Mat imageMat);
public boolean retrieve(Mat imageMat)
{
return nativeRetrieve(mNativeObj, imageMat);
}
public boolean read(Mat imageMat)
{
return nativeRead(mNativeObj, imageMat);
}
我用这个:
private static native boolean nativeRetrieve(long thiz, long imageMat);
private static native boolean nativeRead(long thiz, long imageMat);
public boolean retrieve(Mat imageMat)
{
return nativeRetrieve(mNativeObj, imageMat.getNativeObjAddr());
}
public boolean read(Mat imageMat)
{
return nativeRead(mNativeObj, imageMat.getNativeObjAddr());
}
注意:即使代码在try ... catch中，传递错误的DID类型也不会在c++中触发异常。 try ... catch可能写错了，我不知道。