Use shell pipe or vertical bar "|" with NodeJs spawn()

Question

for encoding a video in ffmpeg and stream to a server, i need to use the pipe "|" command to copy the video before re-encoding it and sending it to the server.

This command works perfectly in the shell :

./ffmpeg  -f x11grab -s 640x480 -framerate 25 -i :0.0 -vcodec libx264 -framerate 25 -rtbufsize 2500k -s 640x480 -preset veryfast -pix_fmt yuv420p -crf 26 -force_key_frames 'expr:gte(t,n_forced*2) -minrate 850k -maxrate 850k -b:v 900k -bufsize 280k -f flv -
| ./ffmpeg -f flv -i - -c copy -f flv "rtmp://SERVER_ADRESS.twitch.tv/app/STREAM_KEY"

In the shell, i see the normal output of ffmpeg, wich contains multiple lines like this:

frame=  218 fps=0.0 q=-1.0 Lsize=    1860kB time=00:00:09.08 bitrate=1677.5kbits/s dup=1 drop=7 speed=11.2x  
frame=  219 fps=0.0 q=-1.0 Lsize=    1860kB time=00:00:10.08 bitrate=1677.5kbits/s dup=1 drop=7 speed=11.2x  
...

Now how to translate it to NODEJS with spawn ? If i do something like this :

var arguments = [
    '-f', 'xgrab',
    '-s', '640x480',  
    '-framerate', '25',
    '-i', ':0.0',
    '-vcodec', 'libx264',
    '-framerate', '25'      
    '-rtbufsize', '2500k',
    '-framerate', framerate,
    '-s', '640x4',50
    '-preset', 'veryfast',
    '-pix_fmt', 'yuv420p',
    '-crf', '26',
    '-force_key_frames', 'expr:gte(t,n_forced*2)',
    '-minrate', 850 +'k',
    '-maxrate',850+'k',
    '-b:v', 900+'k',
    '-bufsize', 280+'k',
    '-f', 'flv',
    '-', '|',
    './ffmpeg', '-f','flv', '-i', '-',
    '-c', 'copy',
    '-f', 'flv', 'rtmp://SERVER_ADRESS.twitch.tv/app/STREAM_KEY'
]);


var childProcess = spawn(cmd, arguments);

childProcess.stdout.on('data', function(data){
    console.log('stream: '+data.toString());
 });
childProcess.stderr.on('data', function(data){
    console.log('stream: '+data.toString());
});

I only get the output from the first part of the command, before the "|" and the 2nd part never runs. Also, i think something disastrous is happening in background because i get multiple instances of ffmpeg on my computer when i check the running processes.

Answer 1

The pipe is a shell construct, so you'll have to do something like:

spawn('/bin/sh', '-c', cmd_plus_arguments_and_pipes);