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• Where does facebook compress its video and Images, Client side or server Side

  20 juillet 2021, par Mohan

  We know that Facebook compress its video and images when we upload it. My question is where does this happen ? If I am uploading the video from my mobile device, does Facebook compress the video using Media Codec or FFmPeg library on native android device (like it is done by WhatsApp) or It first uploads the video on server and then compress the video on server ?

  


• Why process output reader returns null data ? When same code in other process works correct

  26 août 2019, par Владимир Водов

  I try to get output from ffmpeg process but cant get output.
  In another processes and commands it works correctly but output returns immideately when start !

          using (var process = new Process())
  
          {
  
              process.StartInfo = new ProcessStartInfo()
  
              {
  
                  FileName = LinkHelper.IPFS_PATH,
  
                  Arguments = cmd,
  
                  UseShellExecute = false,
  
                  CreateNoWindow = true,
  
                  RedirectStandardOutput = true
  
              };
  
  
  
              process.ErrorDataReceived += FfmpegErrorRecieved;
  
              process.Start();
  
  
  
              using (StreamReader reader = process.StandardOutput)
  
              {
  
                  string output = await reader.ReadToEndAsync();
  
                  Console.WriteLine(output);
  
              }               
  
              process.WaitForExit();
  
          }

  Before output handle !

  Update :
  As szatmary said ffmpeg use output error instead standard output, so when you initialize process.StandartInfo don’t forget initialize property "RedirectStandardError" to TRUE !

  Here is correct code :

  private async Task DetectFFmpegCamerasAsync()
  
      {
  
          var cmd = "-list_devices true -f dshow -i dummy";
  
          using (var process = new Process())
  
          {
  
              process.StartInfo = new ProcessStartInfo()
  
              {
  
                  FileName = LinkHelper.FFMPEG_PATH,
  
                  Arguments = cmd,
  
                  UseShellExecute = false,
  
                  CreateNoWindow = true,
  
                  RedirectStandardError = true
  
              };
  
  
  
              process.Start();
  
  
  
              using (StreamReader reader = process.StandardError)
  
              {
  
                  string output = await reader.ReadToEndAsync();
  
                  Console.WriteLine($"Camera detection output: \n {output}");
  
              }               
  
              process.WaitForExit();
  
          }
  
      }

• subprocess.py returns a File Not Found error

  7 avril 2021, par wasneeplus

  As part of a video analysis script I wanted to find the duration of a video file. For this I found the script offered in the first answer to this question : How to get the duration of a video in Python ?

  


  import subprocess

def get_length(filename):
    result = subprocess.run(["ffprobe", "-v", "error", "-show_entries",
                             "format=duration", "-of",
                             "default=noprint_wrappers=1:nokey=1", filename],
        stdout=subprocess.PIPE,
        stderr=subprocess.STDOUT)
    return float(result.stdout)


  


  This code works fine when my friend runs it in a Jupyter server environment, but when I try it on my laptop the trouble starts.

  


  When I imput the following filename into the function :

  


  filename = "C:\\Users\\benja\\OneDrive - De Haagse Hogeschool\\Onderzoeken 3\\8V.mp4"


  


  I get the following error :

  


      Traceback (most recent call last):&#xA;  File "c:/Users/benja/OneDrive - De Haagse Hogeschool/Onderzoeken 3/python_script.py", line 9, in <module>&#xA;    num_of_frames = math.floor((pf.get_length(filename) - 1)) * 30&#xA;  File "c:\Users\benja\OneDrive - De Haagse Hogeschool\Onderzoeken 3\python_funcs.py", line 21, in get_length&#xA;    stderr=subprocess.STDOUT)&#xA;  File "C:\Users\benja\Anaconda3\lib\subprocess.py", line 466, in run&#xA;    with Popen(*popenargs, **kwargs) as process:&#xA;  File "C:\Users\benja\Anaconda3\lib\subprocess.py", line 769, in __init__&#xA;    restore_signals, start_new_session)&#xA;  File "C:\Users\benja\Anaconda3\lib\subprocess.py", line 1172, in _execute_child&#xA;    startupinfo)&#xA;FileNotFoundError: [WinError 2] Het systeem kan het opgegeven bestand niet vinden&#xA;</module>

  


  I do realise that my problem is almost identical to that of several other questions on here. However, their solutions don't seem to work for me. I have tried to :

  


  

  • Add the location of ffmpeg-win64-4.2.2.exe to the Path system variable.

  


  • Add the location of python.exe to the ComSpec system variable.

  


  • Put the videofile in the same directory as the script.

  


  


  I would be most grateful if someone could point me in the right direction. Thank you in advance.