所以我试图创建一个Android应用程序，它将使用OpenCV通过JNI和NDK逐帧打开视频文件，检测每个帧中的面部并显示它们（最终目标是加速算法，更好地适应糟糕的移动处理。）
我尝试的第一种方法是MediaMetadataRetriever没有结果，它只返回null。
第二种方法是FFMpegMediaMetadataRetriever，它按预期工作，但速度非常慢（最高2fps;太慢），部分原因是你必须从FFMpegMMR的位图转换为Mat然后检测到绘制然后转换回位图，这是我甚至尝试的穴居人。
我目前正在研究的第三种方法是VideoCapture grab（）和retrieve（）。我为本机代码创建了一个包装器，主要是通过从OpenCV示例复制facestector。我也试过read（），据说将两者结合起来，但它也会导致致命的信号11（OpenCV或Android平台的某些上帝级别的分段错误）。
以下是应用程序获取绝对文件路径的方法（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包装器，并且当调用retrieve（）或read（）时发送信号，请注意构造函数open（）和grab（）都可以工作（或者至少不要＃39 ; t崩溃应用程序）。
这是包装器（我已正确传递了VideoCapture对象，我了解到这是导致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);
}
}
这就是它的原生部分（导致错误的确切行是result = ((VideoCapture*)thiz)->retrieve((*((Mat*)imageMat)));，这是方法nativeRetrieve（）
#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，我不知道如何在Eclipse中调试c ++，这就是我使用日志消息查找的原因代码中的错误。那些帮助非常大，因为open（）和grab（）没有工作，我发现并压扁了一个bug，我忘了将thiz传递给方法。 retrieve（）的问题在于我无法为我的生活找到它的来源。在highgui.hpp中有部分定义，但没有实现，我可以在其中放置日志消息来帮助我调试。
可能的解决方案是：
所以，如果有人能告诉我在哪里可以找到retrieve（）和read（）的实现，我将非常感激。或者，如果我错过了一些明显和愚蠢的事情（我希望）。
与此同时，我会尝试在Eclipse中找到一种调试c ++的方法，也许会尝试其他格式？
答案 0 :(得分：1)
最后，根据Aleksander的建议找到它，我设法找到从Java传递给JNI的对象的类型不匹配。
事实证明，错误发生在java部分，其中声明了本机方法。而不是传递Mat，我必须传递Mat.getNativeObjAddr（），这是一个很长的。
所以而不是
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);
}
我用过这个：
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：传递错误的类型DID不会在c ++中触发异常，即使代码是在try ... catch中。尝试捕获可能写错了，我不知道。