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• Gnuplot how to set a variable to standard-input if not passed

  27 août 2020, par DDS

  I have a gnuplot script (plot.script) that is invoked like

  


  C:> ffmpeg -i '.\my_awesome_audio_file.wav' -filter_complex aformat=channel_layouts=mono -acodec pcm_s16le -ar 4000 -f data - | gnuplot -e "fileout='plot';fileformat='png';wid=500;" .\plot.script        


  


  Now I'd want to default filein variable to stdin if it is not passed as argument. This because I want to be able to call this script as a 1-liner command with ffmpeg data generation and also as step-by-step procedure

  


  My idea was to use

  


  if(!exists('filein')){
filein = '-';
}


  


  but this throws warning: Skipping data file with no valid points

  


  if i print the variable datafile I got - (I expected something like stdin).

  


  this is the plot.script script :

  


  
if(!exists('filein')){
    filein = '-';
    }

if (!exists("hei")){
    hei = 4444;
    }
if (!exists("wid")){
    wid = 5555;
    }
if(!exists("fileformat")){
     fileformat = 'png';
     }
if(!exists("fileout")){
     fileout = 'risultato';
   }
   
fileout = fileout . '.' . fileformat;
   
if(!exists("dataformat")){
    dataformat = '%int16';
    }
if(fileformat eq 'png'){
  set terminal png transparent size larghezza,altezza;
  
  }else{
  set terminal fileformat size wid,hei;
  }
  set output fileout;
  unset key;
  unset tics;
  unset border;
  set lmargin 0;
  set rmargin 0;
  set tmargin 0;
  set bmargin 0;


print filein;
plot filein binary filetype=bin format=dataformat endian=little array=1:0 with lines linecolor "0x009900";


  


  But I also want to call this command-by-command :
generate the data-file :

  


  c:> ffmpeg -i '.\my_awesome_audio_file.wav' -filter_complex aformat=channel_layouts=mono -acodec pcm_s16le -ar 4000 -f data audio.dat


  


  plot the data :

  


  c:> gnuplot -e "filein='audio.dat';fileout='plot';fileformat='png';wid=500;" .\plot.script


  


• Converting videos to flv using ffmpeg

  6 janvier 2012, par user703526

  In my c# application, i am writing code for converting any video format to flv format. For this FFMPEG is used.

  Some times an exceptions is occuring like :

  Attempted to read or write protected memory. This is often an indication that other memory is corrupt

  Below is my code from where the exception throwing,

      IntPtr pFormatContext;
  
      FFmpeg.av_register_all();
  
  
  
      int ret;
  
      ret = FFmpeg.av_open_input_file(out pFormatContext, this.Filename, IntPtr.Zero, 0, IntPtr.Zero);
  
  
  
      if (ret < 0)
  
      {
  
          Trace.WriteLine("couldn't open input file");
  
  
  
          FFmpeg.av_free_static();
  
          return;
  
      }
  
  
  
  
  
      try
  
      {
  
          ret = FFmpeg.av_find_stream_info(pFormatContext);
  
  
  
          if (ret < 0)
  
          {
  
              Trace.WriteLine("couldnt find stream informaion");
  
              FFmpeg.av_close_input_file(pFormatContext);
  
              FFmpeg.av_free_static();
  
              return;
  
          }
  
  
  
  
  
          FFmpeg.AVFormatContext formatContext = (FFmpeg.AVFormatContext)Marshal.PtrToStructure(pFormatContext, typeof(FFmpeg.AVFormatContext));
  
  
  
          Duration = formatContext.duration / FFmpeg.AV_TIME_BASE;
  
  
  
          for (int i = 0; i < formatContext.nb_streams; ++i)
  
          {
  
              FFmpeg.AVStream stream = (FFmpeg.AVStream)Marshal.PtrToStructure(formatContext.streams[i], typeof(FFmpeg.AVStream));
  
              FFmpeg.AVCodecContext codec = (FFmpeg.AVCodecContext)Marshal.PtrToStructure(stream.codec, typeof(FFmpeg.AVCodecContext));
  
  
  
              if (codec.codec_type == FFmpeg.CodecType.CODEC_TYPE_VIDEO)
  
              {
  
                  Height = codec.height;
  
                  Width = codec.width;
  
  
  
                          Type = FileType.flv;
  
                          MimeType = "video/x-flv";
  
  
  
              }
  
  
  
          }
  
      }
  
      catch (Exception ex)
  
      {
  
          Trace.WriteLine("FFMpeg failed to understand the file");
  
      }
  
  
  
      FFmpeg.av_close_input_file(pFormatContext);
  
      FFmpeg.av_free_static();
  
  }

  And from the above code this ret = FFmpeg.av_find_stream_info(pFormatContext); line throws memory corrupt exception.
  Please help me to solve this issue.

• How to detetc hardware acceleration in ffmpeg

  19 décembre 2020, par Ali Razmkhah

  I am writing c++ program to screen record by ffmpeg 4.3 ! I need to detect hardware acceleration support such as h264_qsv or h264_nvenc without running ffmpeg.exe !

  


  I explored ffmpeg.exe source code and found no results ! some solutions are deprecated or dose not work on 4.3 !
As instance,

  


  avcodec_find_encoder_by_name("h264_qsv")


  


  returns null even it is exist and works properly !