OpenCV3视频创建进度条--createTrackbar

createTrackbar

1、createTrackbar(trackbarname,winname,*value,count,onTrackbarSlide)

参数名
trackbarname表示进度条名字
winname表示窗口名字
value表示进度条位置的索引
count表示该视频的最大帧数
onTrackbarSlide表示回调函数

2、TrackbarSlide(pos)

void onTrackbarSlide(int pos, void *)   //pos参数由g_slider_position传递
{
    g_cap.set(cv::CAP_PROP_POS_FRAMES, pos);   //从第pos帧开始if (!g_dontset)g_run = 1;  //进入单步模式 g_dontset = 0;      
}

3、实现代码

#include<opencv2\opencv.hpp>
#include<opencv2/imgproc/imgproc.hpp>
#include<opencv2/highgui/highgui.hpp>
#include<iostream>
#include<fstream>
using namespace std;
int g_slider_position = 0;
int g_run = 1, g_dontset = 0;
cv::VideoCapture g_cap;void onTrackbarSlide(int pos, void *)   //pos参数由g_slider_position传递
{
    g_cap.set(cv::CAP_PROP_POS_FRAMES, pos);   //从第pos帧开始if (!g_dontset)g_run = 1;  //进入单步模式 g_dontset = 0;      
}
int main()
{
    cv::namedWindow("Example2_4", cv::WINDOW_AUTOSIZE);g_cap.open("Video1.mp4");assert(g_cap.isOpened());int frames = (int)g_cap.get(cv::CAP_PROP_FRAME_COUNT);int tmpw = (int)g_cap.get(cv::CAP_PROP_FRAME_WIDTH);int tmph = (int)g_cap.get(cv::CAP_PROP_FRAME_HEIGHT);cout << "Video has " << frames << " frames of dimensions( " << tmpw << "," << tmph << ")." <<  endl;cv::createTrackbar("Position", "Example2_4", &g_slider_position, frames, onTrackbarSlide);   //创建一个进度条cv::Mat frame;    //用于读取视频流for (;;){
    if (g_run != 0) {
    g_cap >> frame;   //从g_cap读取一帧if (frame.empty()) break;int current_pos = (int)g_cap.get(cv::CAP_PROP_POS_FRAMES);	//获取下一帧的索引值g_dontset = 1;	//初始值为0，下一步调用回调函数会判断并且将g_run设置为1，就会导致进入单步模式cv::setTrackbarPos("Position", "Example2_4", current_pos);	//设置滚动条位置cv::imshow("Example2_4", frame);   //显示一帧图片g_run -= 1;}char c = (char)cv::waitKey(30);   //等待30ms继续执行程序if (c == 's'){
    g_run = 1; cout << "Single step,run = " << g_run << endl;}if (c == 'r'){
    g_run = -1; cout << "Run mode ,run= " << g_run << endl;}if (c == 27)  //esc的ascll码break;}return 0;
}

总结：一开始会默认读取一帧然后停止，因为g_run初始值等于1，如果执行单步模式，即每次g_run=1都会读取一帧后停止，每次拖动进度条都会获取到g_slider_position的值。然后调用回调函数获取下一帧，默认进入单步模式。当输入r时，g_run=-1,此时循环会不断进行，直到读取到esc或者s。