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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

• encoding by using ffmpeg library

  22 août 2013, par Mustafe

  I am currently developing an application by using ffmpeg library. I have a problem with encoding pcm/raw datas. In ffmpeg/encoding_decoding.c source code, at line 146 in this function :

  buffer_size = av_samples_get_buffer_size(NULL, c->channels, c->frame_size, c->sample_fmt, 0);

  buffer_size is being calculated. My function always returns -22 which states an error. After a little examanation I noticed that in line 1888 at avcodec.h it is stated as following which shows the reason. Since CODEC_CAP_VARIABLE_FRAME_SIZE is set my function returns -22 and my program terminates. In this case the encoding code example in ffmpeg's website also could not work. How can I solve this problem ?

  encoding: set by libavcodec in avcodec_open2(). Each submitted frame except the last must contain exactly frame_size samples per channel. May be 0 when the codec has CODEC_CAP_VARIABLE_FRAME_SIZE set, then the frame size is not restricted. decoding: may be set by some decoders to indicate constant frame size