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• Get MP3 content in C ? ffmpeg or mpg123lib ?

  20 novembre 2014, par Nicolás Múnera

  I’m trying for a personal project of mine to mix two mp3 files into one. I’ve been investigating for a couple of days how to read an mp3 with C and i’ve come up with two libraries, ffmpeg and mpg3lib, unfortunately the documentation is a little bit confusing.

  For now I’m trying to get the content of one MP3 file, I just want to understand which parts are valuable and which parts of the data I get are the ones i’m supposed to mix together. This is what i’ve got so far :

  int cont = 0;
  
  fprintf(stderr, "Starting decode...\n");
  
  while(1)
  
  {
  
           len = fread(buf, sizeof(unsigned char), INBUFF, in);
  
           if(len <= 0)
  
                   break;
  
           inc += len;
  
           ret = mpg123_feed(m, buf, len);
  
  
  
           while(ret != MPG123_ERR && ret != MPG123_NEED_MORE)
  
           {
  
                   ret = mpg123_decode_frame(m, &num, &audio, &bytes);
  
                   if(ret == MPG123_NEW_FORMAT)
  
                   {
  
                       mpg123_getformat(m, &rate, &channels, &enc);
  
                       initwavformat();
  
                       initwav();
  
                       fprintf(stderr, "New format: %li Hz, %i channels, encoding value %i\n", rate, channels, enc);
  
                   }
  
  
  
                   printf("Frame # %d: %s\n",cont,audio);          
  
                   fwrite(audio, sizeof(unsigned char), bytes, out);
  
                   outc += bytes;
  
           }
  
       if(ret == MPG123_ERR){
  
               fprintf(stderr, "Error: %s", mpg123_strerror(m));
  
               break; 
  
       }
  
   cont++;
  
   }

  With this code, I think i’m getting the content of the MP3, but when I print it I just get some weird characters, so I don’t know which strategy i should take.

  Could you guys give me a little bit of advice with this ?

  Thank you !

• Why is my discord.py bot not having voice while being hosted on Heroku ?

  24 juillet 2020, par Flying Thunder

  My bot is all set up and running, everything works, EXCEPT for voice : He joins the channel, but doesnt play audio. I have heard many different claims for what the reason is (no permission to use ffmpeg.exe, missing buildpack, missing dependency, Heroku blocking UDP on free users...) - but i hope that someone here ACTUALLY knows what the problem is, because i couldnt find any definitive reason online.

  


  This is the code of the bot : https://github.com/FlyingThunder/DiscordBot/blob/master/main.py
Everything is working fine on my machine.
This is the only error that Heroku logs gave me :
2020-07-24T06:28:30.329937+00:00 app[worker.1]: PermissionError: [Errno 13] Permission denied: 'res/ffmpeg.exe'

  


  I already tried adding https://github.com/jonathanong/heroku-buildpack-ffmpeg-latest.git to my buildpacks, and i added cffi==1.14.0 to my requirements.txt - both solutions that are supposed to fix this exact issue.

  


• How to pipe rgba data using Node.js to ffmpeg ?

  7 juillet 2015, par Swoth

  Context
  I am developing a small programm that is supposed to render a video, as fast as possible, based on frames captured from a canvas. The animation is rendered to a headless canvas implementation using Rekapi (JavaScript animation framework). The headless canvas is a Node.js module called node-canvas by Automattic. The animation frames are rendered one after another, after each rendering the frame is retrieved using canvas.getImageData().data (Uint8ClampedArray - rgba, faster than canvas.toDataUrl) and put into an array. Every frame is supposed to be send to ffmpeg to create a video.

  Rekapi -> canvas -> getImageData -> array -> ffmpeg

  Problem
  Everything except the transfer of stored rgba-array-data to ffmpeg works. I don’t seem to manage the transport using Node.js. How do I pass my frames to ffmpeg using Node.js and what did I do wrong ?

  What I do
  The code below renders and saves each frame as rgba data to an array. The renderScene-function renders each animation frame.

  console.log("Rendering getImageData, length:"+ videoLength);
  
  var dataArray = [];
  
  function imageDataCallback() {
  
      dataArray.push(context.getImageData(0, 0, 1280, 720).data);
  
  }
  
  rekapi.on('afterUpdate', imageDataCallback);
  
  
  
  var time = Date.now();
  
  renderScene(rekapi);
  
  console.log('Time used: ' + (Date.now() - time) + 'ms;');
  
  rekapi.off('afterUpdate', imageDataCallback);

  I already tried various possibilities to pipe that data to ffmpeg. In general I created a child process in Node.js executing ffmpeg :

  var spawn = require('child_process').spawn;    
  
  var child = spawn('ffmpeg', [
  
          '-pix_fmt', 'rgba',
  
          '-s','1280x720',
  
          '-r', 25,
  
          '-f', 'rawvideo',
  
          '-vcodec', 'rawvideo',
  
          '-i', '-', // read frames from stdin
  
          '-threads', 0, // use all cores
  
          'test.mpg']);

  I also tried using -i pipe:0, which is the same as -i -, just to be sure.
  After process creation i registered for various events to know what happens :

   child.on('error', function(error){
  
      console.log(error);
  
  });
  
  child.stdin.on('data', function (data) {
  
      console.log('data retrieved')
  
  });
  
  child.on('exit', function (code) {
  
      console.log('child exit with code:' + code)
  
  });

  Now I write my array data to the child’s stdin :

  for(var i = 0; i < dataArray.length; ++i){
  
      var buffer = new Buffer(dataArray[i]);
  
      child.stdin.write(buffer);
  
      console.log('wrote: ' + i);
  
  }

  I wrote 25 frames this way. The console displays the following :

  wrote: 24
  
  wrote: 25
  
  events.js:85
  
        throw er; // Unhandled 'error' event
  
              ^
  
  Error: read ECONNRESET
  
      at exports._errnoException (util.js:746:11)
  
      at Pipe.onread (net.js:559:26)

  ffmpeg generated a 0 byte test.mpg and as it seems no definded child-callback (like data) except error has been called. I am not 100% sure about the lifecycle but, as I understood, data should be called each time I write something.

  I am very new to Node.js, thus I might not understand the big picture of it’s child processes.

  Since my reputation is too low I am not allowed to post more than 2 links (first question) and I don’t feel comfortable using non-typed languages like JavaScript.