opencv之VideoCapture与VideoWriter笔记

opencv版本:opencv3.4.1 

1. VideoCapture类 

 作用: 捕获视频文件,图像序列或摄像头;

class VideoCapture
{
public://构造VideoCapture();VideoCapture(const String& filename);//apiPreference参数取值:cv::CAP_FFMPEG or cv::CAP_IMAGES or cv::CAP_DSHOW等VideoCapture(const String& filename, int apiPreference);VideoCapture(int index);//析构virtual ~VideoCapture();//打开视频文件或捕获设备或IP视频流以进行视频捕获virtual bool open(const String& filename);//打开摄像机进行视频捕获virtual bool open(int index);bool open(int cameraNum, int apiPreference);virtual bool open(const String& filename, int apiPreference);//若视频捕获已经被初始化(打开),返回true;virtual bool isOpened() const;//关闭视频文件或捕获设备。virtual void release();//从视频文件或捕获设备中捕获下一帧。virtual bool grab();/*解码并返回抓取的视频帧。image为捕获返回的视频帧,没有帧被捕获image为空;成功不会返回true;*/virtual bool retrieve(OutputArray image, int flag &＃61; 0);//抓取、解码并返回下一个视频帧。virtual bool read(OutputArray image);//设置VideoCapture中的属性。virtual bool set(int propId, double value);//返回指定的VideoCapture属性virtual double get(int propId) const;...
};

测试代码:

int main()
{VideoCapture capture;capture.open("./video/xxx.AVI");if(!capture.isOpened()){std::cout <<"failed to open video!" < frameImg ;if(!frameImg.empty()){imwrite("./video/inc835.jpg", frameImg);break;}}capture.release();return 0;
}

 2. VideoWriter类

 作用: 写视频文件或图像序列;

class VideoWriter
{
public://构造VideoWriter();/*filename:输出视频文件的文件名 fourcc:用于压缩帧的编解码器的4个字符代码。fps:帧率frameSize:帧宽高大小;isColor:非0,编码器将期望并编码彩色帧;否则,灰度帧;*/VideoWriter(const String& filename, int fourcc, double fps,Size frameSize, bool isColor &＃61; true);//apiPreference参数: cv::CAP_FFMPEG or cv::CAP_GSTREAMER等VideoWriter(const String& filename, int apiPreference, int fourcc, double fps,Size frameSize, bool isColor &＃61; true);//析构virtual ~VideoWriter();//打开文件virtual bool open(const String& filename, int fourcc, double fps,Size frameSize, bool isColor &＃61; true);bool open(const String& filename, int apiPreference, int fourcc, double fps,Size frameSize, bool isColor &＃61; true);//若视频输出已经被成功初始化(打开),返回true;virtual bool isOpened() const;//关闭视频输出virtual void release();//写下一帧virtual void write(const Mat& image);virtual bool set(int propId, double value);virtual double get(int propId) const;//将4个字符连接到一个fourcc代码static int fourcc(char c1, char c2, char c3, char c4);protected:Ptr writer;Ptr iwriter;static Ptr create(const String& filename, int fourcc, double fps,Size frameSize, bool isColor &＃61; true);
};

测试代码:

int main()
{VideoCapture inputVideo("./video/INC835.AVI");if(!inputVideo.isOpened()){std::cout <<"----VideoCapture open failed----" < rgb;cv::Mat resultImg;while(1){inputVideo >> frameImg;if(!frameImg.empty()){cv::split(frameImg, rgb); //分离出三通道rgb;for(int i &＃61;0; i <3; i&＃43;&＃43;){#if 1if(i !&＃61; 0){//提取B通道分量rgb[i] &＃61; cv::Mat::zeros(Size(imageW,imageH), rgb[0].type());}#endif//通道合并cv::merge(rgb, resultImg);}outputVideo <}

outputVideo.open(fileName, -1,25.0,Size(imageW,imageH),false);

错误: 调用outputVideo.open出现OpenCV: FFMPEG: tag 0xffffffff/&＃39;&＃xfffd;&＃xfffd;&＃xfffd;&＃xfffd;&＃39; is not found (format &＃39;avi / AVI (Audio Video Interleaved)&＃39;)&＃39;

处理: 将参数2改为使用fourcc生成;具体字段需要根据编码确定;

如: outputVideo.open(fileName, VideoWriter::fourcc(&＃39;M&＃39;,&＃39;J&＃39;,&＃39;P&＃39;,&＃39;G&＃39;),25.0,Size(imageW,imageH),false);

或fourcc(&＃39;F&＃39;,&＃39;M&＃39;,&＃39;P&＃39;,&＃39;4&＃39;)&＃xff1b;

参考: python错误&＃xff1a;OpenCV: FFMPEG: tag 0xffffffff/’&＃xfffd;&＃xfffd;&＃xfffd;&＃xfffd;‘’is not found (format ’mp4 / MP4 (MPEG-4 Part 14)’)’-python黑洞网