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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


  


• Convert wav to mp3 using Meteor FS Collections on Startup

  28 juillet 2015, par TheBetterJORT

  I’m trying to transcode all wav files into a mp3 using Meteor and Meteor FS Collections. My code works when I upload a wav file to the uploader — That is it will convert the wav to a mp3 and allow me to play the file. But, I’m looking for a Meteor Solution that will transcode and add the file to the DB if the file is a wav and exist in a certain directory. According to the Meteor FSCollection it should be possible if the files have already been stored. Here is their example code : *GM is for ImageMagik, I’ve replaced gm with ffmpeg and installed ffmpeg from atmosphereJS.

  Images.find().forEach(function (fileObj) {
  
    var readStream = fileObj.createReadStream('images');
  
    var writeStream = fileObj.createWriteStream('images');
  
    gm(readStream).swirl(180).stream().pipe(writeStream);
  
  });

  I’m using Meteor-CollectionFS [https://github.com/CollectionFS/Meteor-CollectionFS]-

  if (Meteor.isServer) {
  
    Meteor.startup(function () {
  
          Wavs.find().forEach(function (fileObj) {
  
        var readStream = fileObj.createReadStream('.wavs/mp3');
  
        var writeStream = fileObj.createWriteStream('.wavs/mp3');
  
        this.ffmpeg(readStream).audioCodec('libmp3lame').format('mp3').pipe(writeStream);
  
        Wavs.insert(fileObj, function(err) {
  
        console.log(err);
  
      });
  
        });
  
        });
  
  }

  And here is my FS.Collection and FS.Store information. Currently everything resides in one JS file.

  Wavs = new FS.Collection("wavs", {
  
    stores: [new FS.Store.FileSystem("wav"),
  
      new FS.Store.FileSystem("mp3",
  
  
  
      {
  
        path: '~/wavs/mp3',
  
        beforeWrite: function(fileObj) {
  
          return {
  
            extension: 'mp3',
  
            fileType: 'audio/mp3'
  
          };
  
        },
  
        transformWrite: function(fileObj, readStream, writeStream) {
  
          ffmpeg(readStream).audioCodec('libmp3lame').format('mp3').pipe(writeStream);
  
        }
  
      })]
  
  });

  When I try and insert the file into the db on the server side I get this error : MongoError : E11000 duplicate key error index :

  Otherwise, If I drop a wav file into the directory and restart the server, nothing happens. I’m new to meteor, please help. Thank you.

• How can I intercept encoded video data using ffmpeg with C ?

  24 février 2017, par TerNer

  First of all, I hope you’ll understand my poor english skill. I’ll do my best to write question about it.

  I’m currently developing some application. That application will captures desktop and encodes to MP4 video and send mp4 video data/chunks to another clients (all this process should run in memory not file). so another client should can play mp4 video/data/chunks that received from server.

  so I used avio = avio_open(...) and reassigned write function as like avio->write_packet = some_function. but this way seems not "generate" mp4 file/chunk correctly. and It seems the original write_packet callback having actual logic that write packet to a file. but I don’t want to write to a file. so I was thinking about it for a week but I did’t getting any of idea about it.

  so my question is : How can I intercept "encoded" video data that should processed by avio->write_packet ?