调整图像大小后，OpenCV VideWriter无法正常工作 [英] OpenCV VideWriter not working after image resize

问题描述

我正在使用OpenCV 3和Visual Studio. 这里的问题是，除了默认的完整摄像机分辨率外，我无法保存任何特定分辨率的视频. 没有错误，但是视频文件没有增长.它保持在5.54kb.

I am using OpenCV 3 and Visual Studio. The issue here is that I am unable to save video for any particular resolution other than default full camera resolution. There is no error, but video file doesn't grow. It stays at 5.54kb.

这是我的代码:

#include"opencv2\opencv.hpp"
using namespace cv;
using namespace std;

VideoCapture cap_cam1(0);

double Width = cap_cam1.get(CV_CAP_PROP_FRAME_WIDTH);
double Height = cap_cam1.get(CV_CAP_PROP_FRAME_HEIGHT); 
cv::Size frameSize(static_cast<int>(Width), static_cast<int>(Height));
string videoFileName = "D://current.avi";
VideoWriter cam1_write(videoFileName, CV_FOURCC('D', 'I', 'V', '3'), 10.0, frameSize, true);
Mat image;
int main()
{
    while (true)
    {
        cap_cam1 >> image;
        resize(image, image, Size(320, 240));
        imshow("image", image);
        cam1_write.write(image);
        if (waitKey(33) == 27)break;
    }

}

如果删除resize函数，则文件大小会增加，并且会添加框架. 我还尝试在VideoWriter定义之后添加以下行

If I remove the resize function, then file size grows and frames are added. I also tried adding below lines after VideoWriter definition

cap_cam1.set(CV_CAP_PROP_FRAME_WIDTH, 240);
cap_cam1.set(CAP_PROP_FRAME_HEIGHT,320);

在所有文件大小都保持在5.54kb之后，我还尝试了在VideoWriter定义下更改分辨率.

I also tried changing resolution at VideoWriter definition, after everything file size remains at 5.54kb.

如何以自定义分辨率录制视频?

How to record video at custom resolution?

推荐答案

您正在使用

double Width = cap_cam1.get(CV_CAP_PROP_FRAME_WIDTH);
double Height = cap_cam1.get(CV_CAP_PROP_FRAME_HEIGHT);
cv::Size frameSize(static_cast<int>(Width), static_cast<int>(Height));
VideoWriter cam1_write(videoFileName, CV_FOURCC('D', 'I', 'V', '3'), 10.0, frameSize, true);

这意味着您要编写具有VideoCapture图像大小的视频.

which means you want to write a video with the VideoCapture image size.

在这里您必须更改为

cv::Size targetSize = cv::Size(320,240);
VideoWriter cam1_write(videoFileName, CV_FOURCC('D', 'I', 'V', '3'), 10.0, targetSize, true);

现在在您的循环中使用

    resize(image, image, targetSize);

这意味着在创建VideoWriter时必须确定想要的输出图像大小.这是因为典型的编解码器假定图像分辨率不变(已知).

That means you have to decide what kind of output image size you want to have when creating the VideoWriter. That's because typical codecs assume constant (known) image resolution.

要设置分辨率，您需要输入一些错字:

For setting resolution you have some typo:

cap_cam1.set(CV_CAP_PROP_FRAME_WIDTH, 240);
cap_cam1.set(CAP_PROP_FRAME_HEIGHT,320);

这意味着分辨率为cv::Size(240,320)，因此如果将其中的顺序更改为cv::Size(320,240)，则您的代码可能会起作用.查看@MBo的评论

this would mean a resolution of cv::Size(240,320), so your code might work if you changed the order there to cv::Size(320,240). See comment of @MBo

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