有人用OpenCV做多媒体开发，OpenCV这方面比较弱，之所以把视频读取写入这部分做的强大一些，是为了方便大家做视频处理，由于这部分是基于vfw和ffmpeg二次开发的，功能还是很弱。切记一点，OpenCV是一个强大的计算机视觉库，而不是视频流编码器或者解码器。希望大家不要走入这个误区，可以把这部分简单单独看待。目前，OpenCV只支持avi的格式，而且生成的视频文件不能大于2GB，而且不能添加音频。如果你想突破这些限制，建议好好看看ffMpeg，而不是浪费时间在OpenCV上。不过也可以利用视频后期合成工具制作。
三种应用
- 从摄像头读取视频流读取视频帧保存为图片
- 从摄像头读取视频流读取视频帧保存为视频
- 多个视频合成一个视频窗口播放
int readFromCamera()
{
VideoCapture capture(0);//0表示打开默认的摄像头，自动探测
if (!capture.isOpened())
{
cout << "open camera failed..\n" << endl;
return -1;
}
//视频流属性
//VideoCaptureProperties ------> CV_CAP_PROP_XXX
//想要获取视屏对的属性信息，通过get()方法获取
double fps = capture.get(CV_CAP_PROP_FPS);//帧信息
cout << "每秒" << fps << "帧" << endl;
int frameWidth = capture.get(CAP_PROP_FRAME_WIDTH);
int frameHeight = capture.get(CAP_PROP_FRAME_HEIGHT);
cout << frameWidth << "*" << frameHeight << endl;
/* VideoWriter:
The constructors / functions initialize video writers.
- On Linux FFMPEG is used to write videos;
-On Windows FFMPEG or VFW is used;
-On MacOSX QTKit is used.
VideoWriter(const String& filename, int fourcc, double fps,
Size frameSize, bool isColor = true);
*/
//写入的Size()尺寸要和前面读取到的帧尺寸大小相同，否则无法写入视频,大小一直为0KB或者6KB
VideoWriter writer("av_1.avi", CV_FOURCC('D', 'I', 'V', 'X'), 25.0, Size(frameWidth, frameHeight), true);//构造函数方式
//VideoWriter writer;
//writer.open("av_2.avi", CV_FOURCC('D', 'I', 'V', 'X'), 30.0, Size(frameWidth, frameHeight0), true);//调用open函数方式
Mat frame, bgmask;
namedWindow("showVideo", CV_WINDOW_NORMAL);
//Ptr<BackgroundSubtractor> pMOG2 = createBackgroundSubtractorMOG2();
//pMOG2->apply(frame, bgmask, 0.5);
int count = 0;
char imagePath[20];
while (capture.read(frame))
{
imshow("showVideo",frame);
if (count<100)
{
sprintf(imagePath, "E://image//img_%03d.jpg", count);
imwrite(imagePath,frame);//保存前100帧图像
count++;
}
writer.write(frame);//写入视频文件
char a = waitKey(10);//10毫秒内是否退出，27对应键盘的ESC键是否按下
if (a == 27)
{
break;
}
}
writer.release();//释放资源
capture.release();//释放资源
return 0;
}
http://www.fourcc.org/codecs.php 网页列出相应的编码格式
常用的有：
CV_FOURCC('P','I','M','1') = MPEG-1 codec
CV_FOURCC('M','J','P','G') = motion-jpeg codec
CV_FOURCC('M', 'P', '4', '2') = MPEG-4.2 codec
CV_FOURCC('D', 'I', 'V', '3') = MPEG-4.3 codec
CV_FOURCC('D', 'I', 'V', 'X') = MPEG-4 codec
CV_FOURCC('U', '2', '6', '3') = H263 codec
CV_FOURCC('I', '2', '6', '3') = H263I codec
CV_FOURCC('F', 'L', 'V', '1') = FLV1 codec图片写视频流
Mat src=imread("C:\\EXPERIMENT\\眼图照片 (glass)\\wph2\\l0.bmp",1);
char image_name[50];
int isColor = 1;
int fps = 10;
int frameWidth = src.cols;
int frameHeight = src.rows;
VideoWriter writer("C:\\EXPERIMENT\\test_l.avi", VideoWriter::fourcc('M', 'J', 'P', 'G'), fps, Size(frameWidth, frameHeight), isColor);
cout << "info:" << endl
<< "ff.avi" << endl
<< "Size:" << frameWidth << "*" << frameHeight << endl
<< "fps:" << fps << endl;
for (int i = 0; i < 1000; i++)
{
sprintf(image_name, "C:\\EXPERIMENT\\眼图照片(glass)\\wph2\\l%d.bmp", i);
src = imread(image_name, 1);
if (src.empty())
{
MessageBox(NULL, L"全部图像加载完成！", L"温馨提示", MB_OK | MB_ICONINFORMATION);
break;
}
imshow("【src】", src);
waitKey(5);
writer.write(src);
}
多个视频合成视频窗口播放
void mergeVideo()
{
VideoCapture capture1;
VideoCapture capture2;
capture1.open("av_1_1.avi");
capture2.open("av_1_2.avi");
if (!capture1.isOpened() && !capture2.isOpened())
{
cout << "open video1 failed..\n" << endl;
return;
}
Mat frame1, frame2;
VideoWriter writer("av_3.avi", CV_FOURCC('D', 'I', 'V', 'X'), 30.0, Size(640,420), true);
while (capture1.read(frame1) && capture2.read(frame2))
{
Mat result(Size(640, 420),CV_8UC3,Scalar::all(0));
resize(frame1, frame1, Size(640, 210));
resize(frame2, frame2, Size(640, 210));
Mat roi1 = result(cv::Rect(0,0,640, 210));
Mat roi2 = result(cv::Rect(0, 210,640,210));
frame1.copyTo(roi1);
frame2.copyTo(roi2);
imshow("result", result);
writer.write(result);
char a = waitKey(10);//10毫秒内是否退出，27对应键盘的ESC键是否按下
if (a == 27)
{
break;
}
}
capture1.release();
capture2.release();
writer.release();
waitKey(0);
}
参考
https://blog.csdn.net/qq_30241709/article/details/78850225（视频流处理）
