Piping writeable to readable

[asaphaaning]

I want to read from my stream in chunks of 1933 bytes. As I understand, a readablestream can be constructed to emit data upon the internal buffer reaching this given size, however, my ffmpeg call is outputting its processed data into a writable stream, not a readable stream.

I tried piping the writeable stream into a readable stream, both instances of the node-stream-buffer implementation, but that didn't work out.

Is this something that is possible?

[samcday]

Hey @asaphaaning what you're describing should be possible. Can you share some code of what you're trying to achieve and explain where it's not working?

[asaphaaning]

Hey @samcday thanks for answering. I have problems getting ffmpeg to produce any output from events if I specify an output stream, but if I let it create a PassThrough stream by simply calling let stream = cmd.stream() I can successfully listen to events on the stream variable.

That aside, here's what I wanted to achieve:

var ffmpeg = require('fluent-ffmpeg');
var command = ffmpeg();
var streamBuffers = require('stream-buffers');

const width = 24;
const height = 12;
const colors = 3;

var myWritableStreamBuffer = new streamBuffers.WritableStreamBuffer({
	initialSize: width * height * colors * 3, // triple buffering
	incrementAmount: width * height * colors * 3
});

var myReadableStreamBuffer = new streamBuffers.ReadableStreamBuffer({
	frequency: 40, // 25 FPS
	chunkSize: width * height * colors + 13 // 1 full frame - 13 bytes metadata for ppm.
});

let cmd = ffmpeg('/home/haaning/Videos/input.mkv')
	.size(`${width}x${height}`)
	.videoCodec('ppm')
	.outputFormat('image2pipe');

cmd.stream(myWritableStreamBuffer, { end: true });

myWritableStreamBuffer.pipe(myReadableStreamBuffer, { end: true });

myWritableStreamBuffer.on('data', (chunk) => {
	console.log(chunk);
});

myReadableStreamBuffer.on('data', (chunk) => {
	console.log(chunk);
});

This produces an error:

Error: Cannot pipe, not readable

Now, if I try to grab my PassThrough stream like I mentioned in the beginning and pipe that into a ReadableStreamBuffer I get the error dest.write is not a function

var ffmpeg = require('fluent-ffmpeg');
var command = ffmpeg();
var streamBuffers = require('stream-buffers');

const width = 24;
const height = 12;
const colors = 3;

var myWritableStreamBuffer = new streamBuffers.WritableStreamBuffer({
	initialSize: width * height * colors * 3, // triple buffering
	incrementAmount: width * height * colors * 3
});

var myReadableStreamBuffer = new streamBuffers.ReadableStreamBuffer({
	frequency: 40, // 25 FPS
	chunkSize: width * height * colors + 13 // 1 full frame - 13 bytes metadata for ppm.
});

let cmd = ffmpeg('/home/haaning/Videos/input.mkv')
	.size(`${width}x${height}`)
	.videoCodec('ppm')
	.outputFormat('image2pipe');

let stream = cmd.stream();

stream.pipe(myReadableStreamBuffer, { end: true });

myReadableStreamBuffer.on('data', (chunk) => {
	console.log(chunk);
});

[asaphaaning]

I suppose something like this would work though, is this an anti-pattern?

var ffmpeg = require('fluent-ffmpeg');
var command = ffmpeg();
var streamBuffers = require('stream-buffers');

const width = 24;
const height = 12;
const colors = 3;

var myWritableStreamBuffer = new streamBuffers.WritableStreamBuffer({
	initialSize: width * height * colors * 3, // triple buffering
	incrementAmount: width * height * colors * 3
});

var myReadableStreamBuffer = new streamBuffers.ReadableStreamBuffer({
	frequency: 40, // 25 FPS
	chunkSize: width * height * colors + 13 // 1 full frame - 13 bytes metadata for ppm.
});

let cmd = ffmpeg('/home/haaning/Videos/input.mkv')
	.size(`${width}x${height}`)
	.videoCodec('ppm')
	.outputFormat('image2pipe');

let passthrough = cmd.stream();

passthrough.on('data', (chunk) => {
	myReadableStreamBuffer.put(chunk);
});

myReadableStreamBuffer.on('data', (chunk) => {
	console.log(chunk);
});