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• Saving Uncompressed Video Files using OpenCv, Gstreamer, and/or FFMPEG ?

  21 septembre 2022, par adav0033

  I have been trying to implement the cv::VideoWriter function from OpenCV to generate a an uncompressed video file. I started this because of a statement within the OpenCV Documentation which I will link here along with the statement.

  


  cv::VideoWriter::VideoWriter    (   const String &  filename,
int     fourcc,
double  fps,
Size    frameSize,
bool    isColor = true 
)       


  


  "If FFMPEG is enabled, using codec=0 ; fps=0 ; you can create an uncompressed (raw) video file."

  


  Ref. https://docs.opencv.org/3.4/dd/d9e/classcv_1_1VideoWriter.html

  


  However whilst troubleshooting the function I came across the refuting statement,

  


  " VideoCapture and VideoWriter do not provide interface to access raw compressed video stream, except maybe MJPEG in some cases.
Make sure you actually use FFmpeg backend by setting apiPreference parameter : VideoWriter("outfile.avi", cv2.CAP_FFMPEG, ...)"

  


  Ref. https://github.com/opencv/opencv/issues/14573

  


  I am now confused about how I go about writing the cv::VideoWriter function to satisfy the requirements to create an uncompressed video file (.avi) and if it is even possible. If it is not possible how do I achieve the outcome of saving an raw uncompressed video file, as I assume it would use some combination of FFMPEG, OpenCV,or Gstreamer.

  


  Note : My code is implemented in c++

  


• Saving Raw Uncompressed Video Files using OpenCv, Gstreamer, and/or FFMPEG ?

  20 septembre 2022, par adav0033

  I have been trying to implement the cv::VideoWriter function from OpenCV to generate a an uncompressed (raw) video file. I started this because of a statement within the OpenCV Documentation which I will link here along with the statement.

  


  cv::VideoWriter::VideoWriter    (   const String &  filename,
int     fourcc,
double  fps,
Size    frameSize,
bool    isColor = true 
)       


  


  "If FFMPEG is enabled, using codec=0 ; fps=0 ; you can create an uncompressed (raw) video file."

  


  Ref. https://docs.opencv.org/3.4/dd/d9e/classcv_1_1VideoWriter.html

  


  However whilst troubleshooting the function I came across the refuting statement,

  


  " VideoCapture and VideoWriter do not provide interface to access raw compressed video stream, except maybe MJPEG in some cases.
Make sure you actually use FFmpeg backend by setting apiPreference parameter : VideoWriter("outfile.avi", cv2.CAP_FFMPEG, ...)"

  


  Ref. https://github.com/opencv/opencv/issues/14573

  


  I am now confused about how I go about writing the cv::VideoWriter function to satisfy the requirements to create a raw uncompressed video file (.avi) and if it is even possible. If it is not possible how do I achieve the outcome of saving an raw uncompressed video file, as I assume it would use some combination of FFMPEG, OpenCV,or Gstreamer.

  


  Note : My code is implemented in c++

  


• How to stop perl buffering ffmpeg output

  4 février 2017, par Sebastian King

  I am trying to have a Perl program process the output of an ffmpeg encode, however my test program only seems to receive the output of ffmpeg in periodic chunks, thus I am assuming there is some sort of buffering going on. How can I make it process it in real-time ?

  My test program (the tr command is there because I thought maybe ffmpeg’s carriage returns were causing perl to see one big long line or something) :

  #!/usr/bin/perl
  
  
  
  $i = "test.mkv"; # big file, long encode time
  
  $o = "test.mp4";
  
  
  
  open(F, "-|", "ffmpeg -y -i '$i' '$o' 2>&1 | tr '\r' '\n'")
  
          or die "oh no";
  
  
  
  while(<f>) {
  
          print "A12345: $_"; # some random text so i know the output was processed in perl
  
  }
  
  </f>

  Everything works fine when I replace the ffmpeg command with this script :

  #!/bin/bash
  
  
  
  echo "hello";
  
  
  
  for i in `seq 1 10`; do
  
          sleep 1;
  
          echo "hello $i";
  
  done
  
  
  
  echo "bye";

  When using the above script I see the output each second as it happens. With ffmpeg it is some 5-10 seconds or so until it outputs and will output sometimes 100 lines each output.

  I have tried using the program unbuffer ahead of ffmpeg in the command call but it seems to have no effect. Is it perhaps the 2>&1 that might be buffering ?
  Any help is much appreciated.

  If you are unfamiliar with ffmpeg’s output, it outputs a bunch of file information and stuff to STDOUT and then during encoding it outputs lines like

  frame=  332 fps= 93 q=28.0 size=     528kB time=00:00:13.33 bitrate= 324.2kbits/s speed=3.75x

  which begin with carriage returns instead of new lines (hence tr) on STDERR (hence 2>&1).