OpenCV - 在视频播放过程中让滑块更新其位置

Question

我已经选择了"学习OpenCV"并尝试了一些代码示例/练习.在这段代码中,我想让滑块在每次视频帧更改时更新其位置,但由于某种原因它不起作用(图片冻结时使用以下代码):

#include "cv.h"
#include "highgui.h"

int g_slider_position = 0;
CvCapture* g_capture = NULL;

void onTrackbarSlide(int pos)
{
    cvSetCaptureProperty(g_capture, CV_CAP_PROP_POS_FRAMES, pos);
}

int main(int argc, char** argv)
{
    cvNamedWindow("The Tom 'n Jerry Show", CV_WINDOW_AUTOSIZE);
    g_capture = cvCreateFileCapture(argv[1]);
    int frames = (int) cvGetCaptureProperty(
        g_capture, 
        CV_CAP_PROP_FRAME_COUNT
        );

    if (frames != 0)
    {
        cvCreateTrackbar(
            "Position",
            "The Tom 'n Jerry Show",
            &g_slider_position,
            frames,
            onTrackbarSlide
            );
    }

    IplImage* frame;

    while (1)
    {
        frame = cvQueryFrame(g_capture);
        if (!frame) 
            break;

        cvSetTrackbarPos(
            "Position", 
            "The Tom 'n Jerry Show",
            ++g_slider_position
            );

        cvShowImage("The Tom 'n Jerry Show", frame);
        char c = cvWaitKey(33);
        if (c == 27)
            break;
    }

    cvReleaseCapture(&g_capture);
    cvDestroyWindow("The Tom 'n Jerry Show");

    return 0;
}

知道如何让滑块和视频按预期工作吗？

Answer 1

This is the actual working code



// PROGRAM TO ADD A UPDATING TRACKBAR TO A VIDEO

#include <cv.h>
#include <highgui.h>


int g_slider_position = 0;
CvCapture* video_capture = NULL;

void onTrackbarSlide(int current_frame)
{
    current_frame = g_slider_position;
    cvSetCaptureProperty(video_capture,CV_CAP_PROP_POS_FRAMES,current_frame);
}

int main( int argc, char** argv )
{
    cvNamedWindow( "Video", CV_WINDOW_AUTOSIZE );
    video_capture = cvCreateFileCapture( "Crowdy.avi");
    int no_of_frames = (int) cvGetCaptureProperty(video_capture,CV_CAP_PROP_FRAME_COUNT);
    if( no_of_frames!= 0 ) 
    {
        cvCreateTrackbar("Slider","Video",&g_slider_position,no_of_frames,onTrackbarSlide);
    }

    IplImage* frame;

    while(1) 
    {
        frame = cvQueryFrame( video_capture );
        if( !frame ) break;
        cvShowImage( "Video", frame );
        cvSetTrackbarPos("Slider","Video",++g_slider_position);
        char c = cvWaitKey(33);
        if( c == 27 ) break;
    }
    cvReleaseCapture( &video_capture );
    cvDestroyWindow( "Video" );

    return(0);
}

Answer 2

您在代码中递增g_slider_position两次,因此它将增加超出其限制(在cvCreateTrackbaras中设置frames).这可能会导致您的照片冻结.

要修复,请更改此设置

    g_slider_position++;
    cvSetTrackbarPos(
        "Position", 
        "The Tom 'n Jerry Show",
        ++g_slider_position
        );

至

    cvSetTrackbarPos(
        "Position", 
        "The Tom 'n Jerry Show",
        ++g_slider_position
        );

考虑到编辑过的代码,我会检查OpenCV是否正确读取文件中的帧数.查看学习OpenCV的第2章,示例2.3,了解一般从AVI中检索帧数的方法(如果这是您正在使用的).

在上面的代码中,如果帧数为0,则不会创建轨迹栏,但代码仍会进入一个尝试更新轨迹栏位置的循环(如果找到一个框架).我会改用它:

if (frames != 0)
{
    cvCreateTrackbar(
        "Position",
        "The Tom 'n Jerry Show",
        &g_slider_position,
        frames,
        onTrackbarSlide
        );
} 
else
{
    exit(1);
}