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• Programmatically using terminal in linux escapes my command

  21 février 2023, par David Chavez

  Using nodeJS exec function which runs my command from a new process overwrites my backslashes which makes my command invalid. How can I prevent this or use a workaround ?

  


  I need the final command to look like this :
  
...drawtext=text='timestamp \: %{pts \: localtime...

  


  With that code, \: is escaped into :.
  
Using \\: is escaped into \\: while I'm expecting \:

  


  How do I get ...drawtext=text='timestamp \: %{pts \: localtime... to be ran ?

  


  // This command works if pasted directly into terminal
const ffmnpegCode = `ffmpeg -i /path/input.mp4 -y -r 25   -ss 0 -to 124 -c:v libx264 -c:a aac -vf "scale=1920:1080:force_original_aspect_ratio=decrease,pad=1920:1080:(ow-iw)/2:(oh-ih)/2,setsar=1,drawtext=text='timestamp \: %{pts \: localtime \: 1665679092.241 \: %m-%d-%Y %H\\\\\:%M\\\\\:%S}': x=(w-text_w-10): y=(h-text_h-5): fontsize=45: fontcolor=white@0.9: box=1: boxcolor=black@0.6: fontfile='/path/OpenSans-Regular.ttf'" /path/output.mp4`
const encode = async ffmpegCode => {
    try {
        await execPromise(ffmpegCode);
        return 200
    } catch (err) {
        console.log(err)
    }
}


  


  JS adds extra \ which breaks my command

  


• What does the variable ${i%.*} mean in terminal ?

  17 mars 2020, par wongz

  This shell command converts all .avi to .mp4 as per this answer by @llogan

  Can someone explain how $i%.* works ?
  In particular, what does % do ?

  for i in *.avi; do ffmpeg -i "$i" "${i%.*}.mp4"; done

• JPEG quality problems

  26 février 2020, par atokzz

  I am currently using C# to retrieve frames from a borescope (via the FFMPEG library). However, I came across a problem weeks ago and I can’t solve it.

  The images are returned in JPEG format (since the borescope stream is MJPEG).

  Some images come without quality problems, but others come with a strange line in the middle
  followed by random staining. (At the end of the question there is an example of a normal image and one with problems).

  Analyzing the structure of the files, I realized that there are some differences, but I don’t really understand JPEG’s binary structure very well, and I can’t tell what is corrupted.

  Getting to know what is corrupted in the image, which culminates in the quality problem, is very important to me because, through this, I can discard the frame using C#. However, without understanding this problem, I can’t even discard the frame, much less fix it.

  So, having the image without quality problems as a reference, what is the problem with the binary structure of the image with quality problems ?

  Examples :

  JPEG 1 : Image without quality problems

  Image’s preview (just to see the quality, do not download from here)

  JPEG 2 : Image with quality problems

  Image’s preview (just to see the quality, do not download from here)

  It’s possible to look into binary structure of images through online HEX editors like : Online hex editor, Hexed or Hex-works.

  Thank you for reading and have a nice day.