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• #/bin/sh in one line

  27 juillet 2012, par GoodGuyGreg

  I'm working on some Haskell project using FFmpeg. I need to batch create from a media folder with MP4 files and create screenshots from all of them. I got the code and am using it on a terminal in Unix. It works, but how do I make it in one line to be executed in system "xxxx" in Haskell ?

  If not using several system"xx"...

  #/bin/sh
  
  for i in $(ls *.mp4)
  
  do
  
      ffmpeg -i $i -vframes 7 -y -ss 10 -s 150x150 -an -sameq -f image2 -r 1/5  $i%1d.jpg
  
  done

  I tried :

  import System.Cmd
  
  function = do{system "#/bin/sh";
  
  system "for i in $(ls *.mp4)";
  
  system "do";
  
  system "ffmpeg -i $i -vframes 7 -y -ss 10 -s 150x150 -an -sameq -f image2 -r 1/5  $i%1d.jpg";
  
  system "done";}

  but it gives a error :

  -vframes: No such file or directory
  
  /bin/sh: Syntax error: "done" unexpected

• ffmpeg record audio from Xvfb on Centos

  25 mai 2017, par boygiandi

  I’m trying to record audio from Xvfb. And I have some problems :

  1. What’s the different between alsa and pulse. I get confuse
  2. Server Centos have no soud card :

  arecord -l

  arecord : device_list:268 : no soundcards found...

  3. I may have many Xvfb process, how to record video and audio from specific Xvfb process. I checked this https://trac.ffmpeg.org/wiki/Capture/ALSA#Recordaudiofromanapplication but still don’t understand how it works.

  ffmpeg -f alsa -ac 2 -i hw:0,0 -acodec pcm_s16le output.wav

  I seen many command like this, but I don’t know how to get hw:0,0 ( id of sound card ? )

  Please help. Thanks

• Exporting MPEG Transport Stream (.ts) keyframes to images in C/C++ ? Libavcodec / FFMPEG ?

  11 mai 2021, par CyberBully2003

  I have some buffers made up of 188 byte TS packets. When I write them to a file, I can successfully view these .ts files in a video player. MPEG-2/H.264 is the format of the Transport Streams.

  


  Now, I would like to export the keyframes from these Transport Streams buffers (or .ts files) as .jpeg or some other common image format in my C/C++ project.

  


  This is a trivial task from the command line using ffmpeg, where I just feed it the .ts file and some parameters.

  


  However, for the purpose of this project, I would like to accomplish this conversion/exporting of keyframes as images code-side in my current C/C++ directory because the raw bytes from these generated images will be put into another format.

  


  People online seem to recommend using libavcodec. There is an mpegets file in the ffmpeg source that seems like it might have some of the backend to do what I want.

  


  However, the steps needed to achieve this task using the library is not apparent.

  


  I know I could call ffmpeg from C++ and use stdin, but this isn't a preferred solution for this project.

  


  If someone could give me some guidance (and even better some example code) to accomplish this task, it would be greatly appreciated !