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• How to setup a virtual mic and pipe audio to it from node.js

  28 octobre 2018, par Niellles

  Summary of what I am trying to achieve :

  I’m currently doing some work on a Discord bot. I’m trying to join a voice channel, which is the easy part, and then use the combined audio of the speakers in that voice channel as input for a webpage in a web browser. It doesn’t really matter which browser it is as long as it can be controlled with Selenium.

  ---

  What I’ve tried/looked into so far

  My bot so far is written up in Python using the discord.py API wrapper. Unfortunately listening to, as opposed to putting in, audio hasn’t been exactly implemented great − let alone documented − with discord.py. This made me decide to switch to node.js (i.e. discord.js) for the voice channel stuff of my bot.

  After switching to discord.js it was pretty easy to determine who’s talking and create an audio stream (PCM stream) for that user. For the next part I though I’d just pipe the audio stream to a virtual microphone and select that as the audio input on the browser. You can even use FFMPEG from within node.js ¹, to get something that looks like this :

  const Discord = require("discord.js");
  
  const client = new Discord.Client();
  
  
  
  client.on('ready', () => {
  
    voiceChannel = client.channels.get('SOME_CHANNEL_ID');
  
    voiceChannel.join()
  
      .then(conn => {
  
        console.log('Connected')
  
  
  
        const receiver = conn.createReceiver();
  
  
  
        conn.on('speaking', (user, speaking) => {
  
          if (speaking) {
  
            const audioStream = receiver.createPCMStream(user);
  
  
  
            ffmpeg(stream)
  
                .inputFormat('s32le')
  
                .audioFrequency(16000)
  
                .audioChannels(1)
  
                .audioCodec('pcm_s16le')
  
                .format('s16le')
  
                .pipe(someVirtualMic);          
  
          }
  
        });
  
      })
  
      .catch(console.log);
  
    }); 
  
  
  
  client.login('SOME_TOKEN');

  This last part, creating and streaming to a virtual microphone, has proven to be rather complicated. I’ve read a ton of SO posts and documentation on both The Advanced Linux Sound Architecture (ALSA) and the JACK Audio Connection Kit, but I simply can’t figure out how to setup a virtual microphone that will show up as a mic in my browser, or how to pipe audio to it.

  Any help or pointers to a solution would be greatly appreciated !

  ---

  Addendum

  For the past couple of days I’ve kept on looking into to this issue. I’ve now learned about ALSA loopback devices and feel that the solution must be there.

  I’ve pretty much followed a post that talks about loopback devices and aims to achieve the following :

  Simply imagine that you have a physical link between one OUT and one
  IN of the same device.

  I’ve set up the devices as described in the post and now two new audio devices show up when selecting a microphone in Firefox. I’d expect one, but I that may be because I don’t entirely understand the loopback devices (yet).

  The loop back devices are created and I think that they’re linked (if I understood the aforementioned article correctly). Assuming that’s the case the only problem I have to tackle is streaming the audio via FFMPEG from within node.js.

  

• Using a pipe character | with child_process spawn

  19 avril 2020, par Titan

  I'm running nodejs on a raspberry pi and I want to run a child process to spawn a webcam stream.

  



  Outside of node my command is :

  



  raspivid -n -mm matrix -w 320 -h 240 -fps 18 -g 100 -t 0 -b 5000000 -o - | ffmpeg -y -f h264 -i - -c:v copy -map 0:0 -f flv -rtmp_buffer 100 -rtmp_live live "rtmp://example.com/big/test"


  



  With child_process I have to break each argument up

  



  var args = ["-n", "-mm", "matrix", "-w", "320", "-h", "240", "-fps", "18", "-g", "100", "-t", "0", "-b", "5000000", "-o", "-", "|", "ffmpeg", "-y", "-f", "h264", "-i", "-", "-c:v", "copy", "-map", "0:0", "-f", "flv", "-rtmp_buffer", "100", "-rtmp_live", "live", "rtmp://example.com/big/test"];


  



  camera.proc = child.spawn('raspivid', args);


  



  However it chokes on the | character :

  



  error, exit code 64
Invalid command line option (|)


  



  How do I use this pipe character as an argument ?

  


• ffmpeg mp3 encoding result differs between pipe and file creation

  11 octobre 2018, par Jinsung Lee

  I’m making the program by using ffmpeg but stuck in some problem

  Encode to mp3 and file out

  ffmpeg -nostats -loglevel 0 -i example.weba -i albumart.jpg -map 0:0 -map 1:0 -id3v2_version 3 -metadata:s:v title="Album cover" -metadata:s:v comment="Cover (front)" out.mp3

  this works very good but

  Encode to mp3 and pipe out

  ffmpeg -nostats -loglevel 0 -i example.weba -i albumart.jpg -map 0:0 -map 1:0 -id3v2_version 3 -metadata:s:v title="Album cover" -metadata:s:v comment="Cover (front)" -f MP3 - > out.mp3

  using pipe output i got

  ffmpeg -i out.mp3
  
  [mp3 @ 0000000001028980] Header missing

  This error

  I need to get this mp3 data with oneline php shell_exec command

  any solution ?

  Thanks