bomtempi bomtempi - 1 year ago 125
Bash Question

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

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://"

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',
'-b:v', 900+'k',
'-bufsize', 280+'k',
'-f', 'flv',
'-', '|',
'./ffmpeg', '-f','flv', '-i', '-',
'-c', 'copy',
'-f', 'flv', 'rtmp://'

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 Source

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

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