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• 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.

  


• lavu/riscv : AV_READ_TIME cycle counter

  12 septembre 2022, par Rémi Denis-Courmont

  lavu/riscv : AV_READ_TIME cycle counter
  This uses the architected RISC-V 64-bit cycle counter from the
  
  RISC-V unprivileged instruction set.
  In 64-bit and 128-bit, this is a straightforward CSR read.
  
  In 32-bit mode, the 64-bit value is exposed as two CSRs, which
  
  cannot be read atomically, so a loop is necessary to detect and fix up
  
  the race condition where the bottom half wraps exactly between the two
  
  reads.
  

  • [DH] libavutil/riscv/timer.h
  • [DH] libavutil/timer.h

• fftools/ffmpeg : store a separate copy of input codec parameters

  13 août 2022, par Anton Khirnov

  fftools/ffmpeg : store a separate copy of input codec parameters
  Use it instead of AVStream.codecpar in the main thread. While
  
  AVStream.codecpar is documented to only be updated when the stream is
  
  added or avformat_find_stream_info(), it is actually updated during
  
  demuxing. Accessing it from a different thread then constitutes a race.
  Ideally, some mechanism should eventually be provided for signalling
  
  parameter updates to the user. Then the demuxing thread could pick up
  
  the changes and propagate them to the decoder.
  

  • [DH] fftools/ffmpeg.c
  • [DH] fftools/ffmpeg.h
  • [DH] fftools/ffmpeg_opt.c