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• Bash while loop wait until task has completed

  30 juillet 2015, par macmichael01

  I have a bash script that I created to process videos from within a folder and it’s subfolders :

  find . -type f -name '*.mkv' | while read file;
  
  do
  
    ffmpeg -i $file ...
  
  done

  The problem : Instead of the while loop waiting ffmpeg to complete, it continues iterate through the loop. The end result is, files not getting processed. I need a way to have the current while loop iteration to wait until ffmpeg is complete before continuing to the next. Or alternatively a way to queue these items.

  Edit : So The solution when iterating over a set of files is to pass the -nostdin param to ffmpeg. Hope this helps anyone else who might have a similar issue.

  Also file —> $file was a copy/paste typo.

• Why does ffmpeg have to align to the power of 2 when processing crop_left ?

  13 mai 2021, par hansionz

  If performance is considered, why doesn't crop_top \ crop_left \ crop_right perform power-of-two alignment ?
enter image description here

  


• How do I send a mediaStream from the electron renderer process to a background ffmpeg process ?

  26 juillet 2020, par Samamoma_Vadakopa

  Goal (to avoid the XY problem) :

  


  I'm building a small linux desktop application using webRTC, electron, and create-react-app. The application should receive a mediaStream via a webRTC peer connection, display the stream to the user, create a virtual webcam device, and send the stream to the virtual webcam so it can be selected as the input on most major videoconferencing platforms.

  


  Problem :

  


  The individual parts all work : receiving the stream (webRTC), creating the webcam device (v4l2loopback), creating a child process of ffmpeg from within electron, passing the video stream to the ffmpeg process, streaming the video to the virtual device using ffmpeg, and selecting the virtual device and seeing the video stream in a videoconference meeting.

  


  But I'm currently stuck on tying the parts together.
The problem is, the mediaStream object is available inside electron's renderer process (as state in a deeply nested react component, FWIW). As far as I can tell, I can only create a node.js child process of ffmpeg from within electron's main process. That implies that I need to get the mediaStream from the renderer to the main process. To communicate between processes, electron uses an IPC system. Unfortunately, it seems that IPC doesn't support sending a complex object like a video stream.

  


  What I've tried :

  


  


  • starting ffmpeg child process (using child_process.spawn) from within renderer process throws 'fs.fileexistssync' error. Browsing SO indicates that only the main process can start these background processes.

    


  


  • creating separate webRTC connection between renderer and main to re-stream the video. I'm using IPC to facilitate the connection, but offer/answer descriptions aren't reaching the other peer over IPC - my guess is this is due to the same limitations on IPC as before.

    


  


  


  My next step is to create a separate node server on app startup which ingests the incoming RTC stream and rebroadcasts it to the app's renderer process, as well as to a background ffmpeg process.

  


  Before I try that, though, does anyone have suggestions for approaches I should consider ? (this is my first SO question, so any advice on how to improve it is appreciated).