我需要捕获帧由从存储在我的sd Android设备的卡的视频帧（在这种情况下我的仿真器）。我通过NDK使用Android和OpenCV的。我手动推SD卡内的文件SinglePerson.avi通过DDBS（日蚀）的文件浏览器，我用下面的code来读取文件：

I need to capture frame by frame from a video stored in my sd card of the Android device (in this case my emulator). I am using Android and OpenCV through NDK. I pushed manually the file "SinglePerson.avi" inside the sdcard through file explorer of DDBS (eclipse) and I used the code below to read the file:

    JNIEXPORT void JNICALL Java_org_opencv_samples_tutorial4_Sample4Mixed_VideoProcessing(JNIEnv*, jobject)
{
    LOGI("INSIDE VideoProcessing ");

    CvCapture* capture = cvCaptureFromAVI("/mnt/sdcard/SinglePerson.avi");

    IplImage* img = 0;

    if(!cvGrabFrame(capture)){              // capture a frame
        LOGI("Inside the if");
        printf("Could not grab a frame\n\7");
        exit(0);
    }
    img=cvRetrieveFrame(capture);// retrieve the captured frame
    cvReleaseCapture(&capture);

}

问题是，cvGrabFrame（捕获）的结果始终为false。 任何建议正确地打开视频和抢框架？ 在此先感谢

The problem is that cvGrabFrame(capture) results always false. Any suggestion to correctly open the video and grab the frames? Thanks in advance

推荐答案

您所观察的行为可能是由于 cvCaptureFromAVI（）失败。您需要开始编码安全并检查调用你做出回报：

The behavior you are observing is probably due to cvCaptureFromAVI() failing. You need to start coding safely and check the return of the calls you make:

CvCapture* capture = cvCaptureFromAVI("/mnt/sdcard/SinglePerson.avi");
if (!capture)
{
    printf("!!! Failed to open video\n\7");
    exit(0);
}

这个功能通常失败，原因有二：

This function usually fails for 2 reasons:

当它是无法访问文件（由于错误的文件系统权限）; （不被OpenCV的支持或视频格式）在缺少$ C $系统上的CCS。 When it's unable to access the file (due to wrong filesystem permissions); Missing codecs on the system (or the video format is not supported by OpenCV).

如果你是新的OpenCV的，我建议你桌面（PC）第一个测试你的OpenCV code。

If you are new to OpenCV, I suggest you test your OpenCV code on a desktop (PC) first.