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• playback speed of ffmpeg-stitched python video plots

  30 juin 2012, par user1211129

  I've been generating videos out of plots made with matplotlib using a line of ffmpeg code. The output is in .mp4 format. However, when I tried to heighten the resolution of each individual plot to dpi=800, the resultant video (at 140 MB) lags severely when played back with quicktime. Is there a way around this ? I do wonder, if the file's too large to play efficiently, why does a movie of 6 GB play flawlessly ?

• OpenCV : FFMPEG : tag is not supported with codec id 12 and format 'mp4 / MP4

  30 septembre 2023, par Tina J

  I was trying to run a repo located HERE. Basically, just targeting SimpleVideoSummarizer.cc which uses OpenCV for some basic video processing. I'm using Ubuntu 14.04. Following is the save part of the code :

  



  void SimpleVideoSummarizer::playAndSaveSummaryVideo(char* videoFileSave) {&#xA;    cv::VideoCapture capture(videoFile);&#xA;    cv::Mat frame;&#xA;    capture.set(CV_CAP_PROP_POS_FRAMES, 0);&#xA;    cv::VideoWriter videoWriter;&#xA;    if (videoFileSave != "") {&#xA;        videoWriter = cv::VideoWriter(videoFileSave, CV_FOURCC(&#x27;M&#x27;, &#x27;J&#x27;, &#x27;P&#x27;, &#x27;G&#x27;), static_cast<int>(capture.get(CV_CAP_PROP_FPS)), cv::Size(capture.get(CV_CAP_PROP_FRAME_WIDTH), capture.get(CV_CAP_PROP_FRAME_HEIGHT)));&#xA;    }&#xA;    for (std::set<int>::iterator it = summarySet.begin(); it != summarySet.end(); it&#x2B;&#x2B;) {&#xA;        capture.set(CV_CAP_PROP_POS_FRAMES, segmentStartTimes[*it] * frameRate);&#xA;        for (int i = segmentStartTimes[*it]; i &lt; segmentStartTimes[*it &#x2B; 1]; i&#x2B;&#x2B;) {&#xA;            for (int j = 0; j &lt; frameRate; j&#x2B;&#x2B;) {&#xA;                capture >> frame;&#xA;                cv::putText(frame, "Time: " &#x2B; IntToString(i) &#x2B; " seconds", cvPoint(30, 30),&#xA;                            cv::FONT_HERSHEY_COMPLEX_SMALL, 0.8, cvScalar(200, 200, 250), 1, CV_AA);&#xA;                if (frame.data) {&#xA;                    cv::imshow("Summary Video", frame);&#xA;                }&#xA;                if (videoFileSave != "") {&#xA;                    videoWriter.write(frame);&#xA;                }&#xA;                // Press  ESC on keyboard to exit&#xA;                char c = static_cast<char>(cv::waitKey(25));&#xA;                if (c == 27) {&#xA;                    break;&#xA;                }&#xA;            }&#xA;        }&#xA;    }&#xA;    capture.release();&#xA;}&#xA;</char></int></int>

  



  I pass an input.mp4 file and specify a out.mp4 as well. Unfortunately, when the example is trying to save the output video file, it throws errors on the FOURCC :

  



  OpenCV: FFMPEG: tag 0x44495658/'XVID' is not supported with codec id 12 and format 'mp4 / MP4 (MPEG-4 Part 14)'
OpenCV: FFMPEG: fallback to use tag 0x7634706d/'mp4v'


  



  or another one :

  



  OpenCV: FFMPEG: tag 0x3234504d/'MP42' is not supported with codec id 15 and format 'mp4 / MP4 (MPEG-4 Part 14)'
[mp4 @ 0x16bc700] Could not find tag for codec msmpeg4v2 in stream #0, codec not currently supported in container


  



  I tried to change the FOURCC in this part of the code which writes the video, and applied XVID, MJPG, X264, MP42, MP4V. None worked and threw similar errors.

  



  What is the problem ? How to fix it ?

  


• cv::VideoWriter Class Failing to Write Frames to Video File

  23 septembre 2022, par adav0033

  I am attempting to using the OpenCV VideoWriter class to save a two camera video feed to a single video file. I am using the FFMPEG API to ahcieve the desired outcome and am trying to generate an .mkv file with the Fourcc code FFV1 for lossless frame writing. Currently I am expriencing upon launching of the pipeline the file writer is creating a file in the directory specified and upon completion of the pipeline the writer is transformed into a video file .mkv however no frames are being written to said file.
My constructor :

  


  cv::VideoWriter writer(out_vid_name + ".mkv", cv::VideoWriter::fourcc('F','F','V','1'), cam_fps,frame_double_size, true);


  


  Note that cv::Size(3840,1080) = frame_double_size and cam_fps is a param

  


  My video capture :

  


  cv::VideoCapture cap(out_vid_name + ".mkv", cv::CAP_FFMPEG);


  


  and my writer :

  


  while (controller->running && ros::ok()) //Shutdown race condition exists. One thread will have to be SIGTERM'ed
        {
            std::shared_lock guard(doubleSaveFrame->mtx);
            doubleSaveFrame->cond_var.wait(guard, [&]{ return doubleSaveFrame->cond_bool_save; });
            doubleSaveFrame->cond_bool_save = false;
            std_msgs::String msg;
            msg.data = std::to_string(frame_count);
            frame_count++;
            frame_pub.publish(msg);

            writer.write(doubleSaveFrame->getHost());
            cv::Mat frame = doubleSaveFrame->getHost();
            int rows = frame.rows;
            int cols = frame.cols;
            std::cout << "rows: " << std::to_string(rows) << " cols: "<< std::to_string(cols) << std::endl;
            cv::imwrite("home/Documents/camera/imwritefun"+ std::to_string(frame_count) +".JPG", doubleSaveFrame->getHost());
        }
        writer.release();


  


  Note that this code above produced successfully the camera frames to file when cv::imwrite was executed, however the the writer failed to write to video file. I am very new to OpenCV and the associated methods used here, if anyone has an idea on what is causing the issue that would be extremely helpful as research has not prevailed a solution.