使用 openCV 编写视频 - 没有为轨道 0 设置关键帧 [英] Writing video with openCV - no key frame set for track 0

问题描述

我正在尝试使用以下代码使用 openCV 2.4.6.1 修改和编写一些视频:

I'm trying to modify and write some video using openCV 2.4.6.1 using the following code:

cv::VideoCapture capture( video_filename );

    // Check if the capture object successfully initialized
    if ( !capture.isOpened() ) 
    {
        printf( "Failed to load video, exiting.\n" );
        return -1;
    }

    cv::Mat frame, cropped_img;

    cv::Rect ROI( OFFSET_X, OFFSET_Y, WIDTH, HEIGHT );


    int fourcc = static_cast<int>(capture.get(CV_CAP_PROP_FOURCC));
    double fps = 30;
    cv::Size frame_size( RADIUS, (int) 2*PI*RADIUS );
    video_filename = "test.avi";
    cv::VideoWriter writer( video_filename, fourcc, fps, frame_size );

    if ( !writer.isOpened() && save )
    {
        printf("Failed to initialize video writer, unable to save video!\n");
    }

    while(true)
    {   
        if ( !capture.read(frame) )
        {
            printf("Failed to read next frame, exiting.\n");
            break;
        }

        // select the region of interest in the frame
        cropped_img = frame( ROI );                 

        // display the image and wait
        imshow("cropped", cropped_img);

        // if we are saving video, write the unwrapped image
        if (save)
        {
            writer.write( cropped_img );
        }

        char key = cv::waitKey(30);

当我尝试使用 VLC 运行输出视频test.avi"时，出现以下错误:avidemux 错误:没有为轨道 0 设置关键帧.我使用的是 Ubuntu 13.04，我尝试使用编码的视频使用 MPEG-4 和 libx264.我认为修复应该很简单，但找不到任何指导.实际代码可在 https://github.com/benselby/robot_nav/tree/master 获得/video_unwrap.提前致谢！

When I try to run the output video 'test.avi' with VLC I get the following error: avidemux error: no key frame set for track 0. I'm using Ubuntu 13.04, and I've tried using videos encoded with MPEG-4 and libx264. I think the fix should be straightforward but can't find any guidance. The actual code is available at https://github.com/benselby/robot_nav/tree/master/video_unwrap. Thanks in advance!

推荐答案

这似乎是写入的帧与打开的 VideoWriter 对象之间大小不匹配的问题.我在尝试将网络摄像头中的一系列调整大小的图像写入视频输出时遇到了这个问题.当我删除调整大小步骤并从初始测试帧中获取大小时，一切正常.

This appears to be an issue of size mismatch between the frames written and the VideoWriter object opened. I was running into this issue when trying to write a series of resized images from my webcam into a video output. When I removed the resizing step and just grabbed the size from an initial test frame, everything worked perfectly.

为了修复我调整大小的代码，我基本上在我的处理过程中运行了一个测试帧，然后在创建 VideoWriter 对象时拉取了它的大小:

To fix my resizing code, I essentially ran a single test frame through my processing and then pulled its size when creating the VideoWriter object:

#include <cassert>
#include <iostream>
#include <time.h>

#include "opencv2/opencv.hpp"

using namespace cv;

int main()
{
    VideoCapture cap(0);
    assert(cap.isOpened());

    Mat testFrame;
    cap >> testFrame;
    Mat testDown;
    resize(testFrame, testDown, Size(), 0.5, 0.5, INTER_NEAREST);
    bool ret = imwrite("test.png", testDown);
    assert(ret);

    Size outSize = Size(testDown.cols, testDown.rows);
    VideoWriter outVid("test.avi", CV_FOURCC('M','P','4','2'),1,outSize,true);
    assert(outVid.isOpened());

    for (int i = 0; i < 10; ++i) {
        Mat frame;
        cap >> frame;

        std::cout << "Grabbed frame" << std::endl;

        Mat down;
        resize(frame, down, Size(), 0.5, 0.5, INTER_NEAREST);

        //bool ret = imwrite("test.png", down);
        //assert(ret);
        outVid << down;


        std::cout << "Wrote frame" << std::endl;
        struct timespec tim, tim2;
        tim.tv_sec = 1;
        tim.tv_nsec = 0;
        nanosleep(&tim, &tim2);
    }
}

我的猜测是你的问题出在尺寸计算上:

My guess is that your problem is in the size calculation:

cv::Size frame_size( RADIUS, (int) 2*PI*RADIUS );

我不确定您的帧来自哪里(即如何设置捕获)，但很可能在舍入或其他地方您的尺寸被弄乱了.我建议做一些类似于我上面的解决方案.

I'm not sure where your frames are coming from (i.e. how the capture is set up), but likely in rounding or somewhere else your size gets messed up. I would suggest doing something similar to my solution above.

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