cvCreateVideoWriter - 无法在后续调用中更改文件名

时间：2011-08-16 17:09:06

标签： c opencv

OpenCV 2.2 Windows 7

我有一个C ++方法（下面），它从一个帧数组（IplImage *）创建一个avi文件。文件名基于两个线程中的哪一个（让我们称之为“左”和“右”）进行写作。

代码：

void AvtCameraCapture::save_as_video(IplImage **frames,const char * fname, int num_frames, int playback_fps,CvSize &size)
{
    //EnterCriticalSection(&cs); 

    CvVideoWriter *writer = cvCreateVideoWriter(fname,CV_FOURCC('D', 'I', 'B', ' '),playback_fps,size);
    printf("Writer is %x\n", writer);
    for (int i=0; i < num_frames; i++) 
    {
        printf("Wrote frame %d to file %s\n",i,fname);
        cvWriteFrame(writer,frames[i]);
    }
    cvReleaseVideoWriter(&writer);

    //LeaveCriticalSection(&cs);
}

为执行该方法的第一个线程创建文件。但是，没有为第二个线程创建文件。

我看到两个线程的打印件，每个线程都有正确的文件名。请注意，CvVideoWriter *是非空的。

writing to file c:\flyball_passes\Left_dog_2.avi
Writer is 4dabf60
Wrote frame 0 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 1 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 2 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 3 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 4 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 5 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 6 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 7 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 8 to file c:\flyball_passes\Left_dog_2.avi
writing to file c:\flyball_passes\Right_dog_2.avi
Writer is 4d2a930
Wrote frame 0 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 1 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 2 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 3 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 4 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 5 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 6 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 7 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 8 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 9 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 10 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 11 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 12 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 13 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 14 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 15 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 16 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 17 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 18 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 19 to file c:\flyball_passes\Right_dog_2.avi
video written to file c:\flyball_passes\Right_dog_2.avi
Masking for 2.696000 seconds in lane Right.
Wrote frame 9 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 10 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 11 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 12 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 13 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 14 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 15 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 16 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 17 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 18 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 19 to file c:\flyball_passes\Left_dog_2.avi
video written to file c:\flyball_passes\Left_dog_2.avi

如果我取消注释Enter / Exit关键部分，一个线程在另一个线程开始之前完成写入，但仍然没有为最后到达的线程创建文件：

writing to file c:\flyball_passes\Left_dog_2.avi
Writer is 4f5d298
Wrote frame 0 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 1 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 2 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 3 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 4 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 5 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 6 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 7 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 8 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 9 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 10 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 11 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 12 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 13 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 14 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 15 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 16 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 17 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 18 to file c:\flyball_passes\Left_dog_2.avi
Wrote frame 19 to file c:\flyball_passes\Left_dog_2.avi
video written to file c:\flyball_passes\Left_dog_2.avi
Masking for 2.570000 seconds in lane Left.
writing to file c:\flyball_passes\Right_dog_2.avi
Writer is 4f5d298
Wrote frame 0 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 1 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 2 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 3 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 4 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 5 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 6 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 7 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 8 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 9 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 10 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 11 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 12 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 13 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 14 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 15 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 16 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 17 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 18 to file c:\flyball_passes\Right_dog_2.avi
Wrote frame 19 to file c:\flyball_passes\Right_dog_2.avi
video written to file c:\flyball_passes\Right_dog_2.avi

即使我等待几秒钟来启动触发第二个文件写入的事件，它也不会显示出来。

如果我只触发触发右侧车道文件写入的事件（左侧车道没有事先调用cvCreateVideoWriter），我会看到右侧车道的avi文件。

非常感谢任何见解！

谢谢，

戴夫托马斯

1 个答案:

答案 0 :(得分：1)

您正在从单独的线程调用OpenCV函数。由于OpenCV 不是线程安全的，因此无法保证您的系统正常运行。

使用互斥锁或其他一些机制来保护正在线程上执行的OpenCV调用。

您应该保护整个代码块不会同时执行：

// lock global mutex

CvVideoWriter *writer = cvCreateVideoWriter(fname,CV_FOURCC('D', 'I', 'B', ' '),playback_fps,size);
printf("Writer is %x\n", writer);
for (int i=0; i < num_frames; i++) 
{
    printf("Wrote frame %d to file %s\n",i,fname);
    cvWriteFrame(writer,frames[i]);
}
cvReleaseVideoWriter(&writer);

// unlock mutex
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