Reading a Continuous Stream of Binary Data in NodeJS

Question

I am trying to read in large volumes of binary data from a stream (created form a child process) in Node. I am using the stdout.on('data') event for my process to get the data.
No matter how much I search, I can't seem to find any docs on the arguments that are passed in to the callback. typeof(data) says it's an object, but from what I can tell, it is just an array.

Is it an array? Or a string? Whatever it is, how can I get an array of bytes out?
Here's my code:

var childProc = require('child_process'),
    spawn = childProc.spawn;

// /home/ubuntu/bin/ffmpeg -f video4linux2 -r 1 -s 640x480 -i /dev/video0 -c:v rawvideo -f rawvideo -pix_fmt rgb8 -

var streamProc = spawn('/home/ubuntu/bin/ffmpeg', [
    '-f', 'video4linux2',
    '-r', '1',
    '-s', '640x480',
    '-i', '/dev/video0',
    '-c:v', 'rawvideo',
    '-f', 'rawvideo',
    '-pix_fmt', 'rgb24',
    '-'
    ]);

streamProc.stdout.on('data', function(data) {

    var bytes = [];

    //Do some magical conversion here to populate the array

    //debugger;
    console.log('OUT: ' + bytes.join()); //Just some debugging steps
});

streamProc.stderr.on('data', function(data) {
    //debugger;
    if(process.argv.indexOf('showerr') != -1)
        console.log('ERR: ' + data);
});

streamProc.on('close',function(exitCode) {
    console.log('EXT: Program exited with code ' + exitCode);
});

Am I missing something obvious?

Andrey Sidorov · Accepted Answer · 2013-10-11 00:54:27Z

1

It's Buffer instance

Also take a look at NodeBasicFFMPEG, ffmpeg-node, node-fluent-ffmpeg

Note that "data" event gives you just a chunk of data, you might need to re-assemble it yourself using something like bufferlist library

answered Oct 11, 2013 at 0:54

Andrey Sidorov

25.6k5 gold badges65 silver badges78 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Wasabi Fan Over a year ago

I can take a closer look, but I already looked at most of the node modules for FFMPEG. I would need one that works on an ARM machine, and I decided it would be easier to just write it out as a child process.

Wasabi Fan Over a year ago

This might just be me being stupid, but shouldn't typeof(data) return 'Buffer' if it was created internally from a class?

Andrey Sidorov Over a year ago

data.constructor.name == 'Buffer'. typeof always return 'object' for objects, try it with function F() { this.foo = 1; }; f = new F(); console.log(typeof(f))

Wasabi Fan Over a year ago

I see... I made the assumption that typeof would give me the same thing as some debuggers do... my mistake! As a side note, any idea if there is an output limit on a child process? It stops the stream of data half way through one burst; and then it stops sending data altogether.

Andrey Sidorov Over a year ago

There is no limit afaik. For example, I use socat process to connect to unix abstract socket and can exchange megabytes without a problem

Collectives™ on Stack Overflow

Reading a Continuous Stream of Binary Data in NodeJS

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related