[学习OpenCV攻略][005][视频播放控制]

cvSetCaptureProperty(视频,属性,属性值)

设置视频的属性，属性可以是宏CV_CAP_PROP_POS_FRAMES 视频帧的位置

cvGetCaptureProperty(视频,属性)

得到视频的属性值，属性可以是宏CV_CAP_PROP_FRAMES_COUNT视频帧数，CV_CAP_PROP_FRAME_WIDTH视频的宽度，CV_CAP_PROP_FRAME_HEIGHT

cvCreateTrackbar(滚动条名称,窗口名称,滑动条位置,总帧数,回调函数)

在窗口中创建滚动条，并设置位置和总帧数，当滚动条被拖动时，触发回调函数

cvSetTrackbarPos(滚动条名称,窗口名称,位置)

设置窗口中滚动条的位置

#include <stdio.h>
#include <iostream>
#include <fstream>
#include "cv.h"
#include "highgui.h"
 
using namespace std;
 
int g_slider_position = 0;
CvCapture* g_capture = NULL;
 
void onTrackbarSlide(int pos){
    cvSetCaptureProperty(
        g_capture,
        CV_CAP_PROP_POS_FRAMES,
        pos
    );
}
 
int getAVIFrames(char * fname) { 
    char tempSize[4];
    // Trying to open the video file
    ifstream  videoFile( fname , ios::in | ios::binary );
    // Checking the availablity of the file
    if ( !videoFile ) {
      cout << "Couldn’t open the input file " << fname << endl;
      exit( 1 );
    }
    // get the number of frames
    videoFile.seekg( 0x30 , ios::beg );
    videoFile.read( tempSize , 4 );
    int frames = (unsigned char ) tempSize[0] + 0x100*(unsigned char ) tempSize[1] + 0x10000*(unsigned char ) tempSize[2] +    0x1000000*(unsigned char ) tempSize[3];
    videoFile.close(  );
    return frames;
}
 
int main(int argc, char** argv){
    cvNamedWindow("hello", CV_WINDOW_AUTOSIZE);
    g_capture = cvCreateFileCapture(argv[1]);
    IplImage *foo = cvQueryFrame(g_capture);
     
    int frames = (int)cvGetCaptureProperty(
        g_capture,
        CV_CAP_PROP_FRAME_COUNT
    );
     
    int tmpw = (int)cvGetCaptureProperty(
        g_capture,
        CV_CAP_PROP_FRAME_WIDTH
    );
     
    int tmph = (int)cvGetCaptureProperty(
        g_capture,
        CV_CAP_PROP_FRAME_HEIGHT
    );
     
    printf("opencv frames %d w %d h %d\n", frames, tmpw, tmph);
     
    frames = getAVIFrames(argv[1]);
     
    printf("hacked frames %d w %d h %d\n", frames, tmpw, tmph);
     
    cvCreateTrackbar(
        "position",
        "hello",
        &g_slider_position,
        frames,
        onTrackbarSlide
    );
     
    IplImage *frame;
    frames = 0;
    while(1){
        frame = cvQueryFrame(g_capture);
        if(!frame){
            break;
        }
         
        frames++;
        printf("\nFrame number=%d", frames);
        cvSetTrackbarPos("position", "hello", frames);
         
        cvShowImage("hello", frame);
         
        char c = (char)cvWaitKey(10);
        if(c == 27){
            break;
        }
    }
     
    cvReleaseCapture(&g_capture);
    cvDestroyWindow("hello");
     
    return 0;
}