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• ctrl+c doesn't wait for child process (background process) to finish with trap

  11 avril 2019, par phisch

  I have a script which registers a SIGINT trap and starts a ffmpeg background process that records part of the screen. The SIGINT trap sends a SIGINT signal to the background ffmpeg process to get it to gracefully stop and finish the recording.

  When this script is run in a terminal, and terminated from a separate terminal with kill -INT [SCRIPT_PID], the ffmpeg background process terminates gracefully and outputs confirmation in terminal 1.

  When the script is run in a terminal and stopped with ctrl+c the background process just dies instantly. (even if ctrl+c should just send a SIGINT signal)

  Why does ctrl+c behave differently than killing the script with kill -INT in this case ?
  How can i make sure the ffmpeg background process ends gracefully when ending the script with ctrl+c ?

  #!/bin/bash
  
  
  
  exit_script() {
  
      kill -INT $ffmpeg_pid
  
      wait $ffmpeg_pid
  
      printf "\n\nffmpeg should say 'exiting normally, received signal 2' before this message is printed!\n\n"
  
  }
  
  
  
  trap exit_script SIGINT 
  
  
  
  ffmpeg -f x11grab -s 500x500 -i :0.0+0,0 ~/video_`date +%s`.webm &
  
  ffmpeg_pid=$!
  
  
  
  wait

  edit : it seems like ffmpeg receives 2 int signals in the case of ctrl+c, but i don’t know why

• When I run `ffmpeg` in the background, how do I prevent `suspended (tty output)` ?

  4 novembre 2017, par Jim DeLaHunt

  I have a sh script which calls ffmpeg on several files. When I try to run this script in the background, redirecting output to a file, the job starts but then immediately suspends :

  % bin/mp3convert.sh path/a/b &> ~/tmp/log.txt &
  
  [1] 93352
  
  % 
  
  [1]  + suspended (tty output)  bin/mp3convert.sh path/a/b &> 

  If I try making the script continue in the background, it immediately suspends again :

  % jobs
  
  [1]  + suspended (tty output)  bin/mp3convert.sh path/a/b &> 
  
  % bg %1
  
  [1]  + continued  bin/mp3convert.sh path/a/b &> 
  
  % jobs
  
  [1]  + suspended (tty output)  bin/mp3convert.sh path/a/b &> 
  
  %

  I can make the script continue, by making it the foreground, but then my terminal is occupied until the script finishes. That means I don’t get the benefit of running the script in the background.

  % 
  
  [1]  + suspended (tty output)  bin/mp3convert.sh path/a/b &> 
  
  % fg %1
  
  [1]  + continued  bin/mp3convert.sh path/a/b &> 
  
  % # much time passes with no activity on terminal, then script finishes
  
  %

  How can I make the script run cleanly in the background ?

  A simplified version of my script is :

  #!/bin/sh
  
  # mp3convert.sh
  
  for f in "$1"/*.flac; do
  
      ffmpeg -i "$f" -c:v copy path/to/dest/"$(basename -s .flac "$f")".mp3
  
  done

  I am running on Mac OS X 10.11.6, with ffmpeg version 3.4 supplied by MacPorts.

  An apparently related question is why do I get “Suspended (tty output)” in one terminal but not in others ?. The answer there is to set the terminal state with stty -tostop. That didn’t help me ; I already had that state set.

• One subtitle "page" to Image via FFMPEG

  12 mai 2017, par Edwin

  I love FFMPEG since it can do so much. But one thing I have been wondering. Is it actually possible to have one subtitle page converted into a transparent (PNG) image ?

  I know I can embed (burn) an SRT stream into a video. It can export to images. So, I think it must be doable, right ?

  Also, if I just through a line of text in the command line, can I just use a subtitle codec to interpret the text and convert it to an image ?

  I would love to make use of certain text styles, like Italic and text colors, stuff like that.

  I thought, I will just ask here before I try for a week (like I am kinda doing now) without any luck :)