pcm-transform

A transform stream that reads PCM data and transforms with built-in or custom functions.

Batches up samples from a PCM stream to a configurable amount (batchSize) and passes them into a configurable transform function so that they can be processed by proximity, like for making waveform data for visualizations.

Install

npm install pcm-transform

Usage

var fs = require("fs");
var lame = require("lame");
var PCMTransform = require("pcm-transform");
 
fs.createReadStream("TesseracT - Concealing Fate, Part One: Acceptance.mp3")
  .pipe(new lame.Decoder)
  .pipe(PCMTransform({ batchSize: 20000 })
  .pipe(fs.createWriteStream("waveform.data");
 

API

PCMTransform()

Constructor for a transform stream. Takes the following config options:

• batchSize - Number of samples to batch together to be transformed. If using 16 bit samples in stereo (2 channels), each sample would be 4 bytes. (required)
• json - Whether or not to write downstream a buffer than is JSON.parse'able. (default: false). See Rendering JSON section later.
• inputChannels - Number of channels on the input PCM stream. (default: 2)
• inputBitDepth - Number of bits per sample (per channel). (default: 16)
• outputBitDepth - Number of bits per value for output. Used to convert buffers from transform functions into JSON. (default: inputBitDepth)
• transform - Either a string name of a default transform (min-max), or a supplied transform function. The function takes as arguments buffer, stream, and callback. Any error or data passed into the callback gets emitted, or written downstream, accordingly. See #custom%20transforms for more info.
• head - A buffer or string that gets written downstream when the streaming starts.
• tail - A buffer or string that gets written downstream when the streaming completes.

Transforms

min-max

Takes the batch of samples and returns the min and max value amongst all samples (regardless of channel) per batch. Results in a buffer of data with sequences of min/max pairs in the form of:

MIN_1 MAX_1 MIN_2 MAX_2 .... MIN_N MAX_N

This is similar to audiowaveform format.

Custom Transforms

TODO

JSON Rendering

Specifying json: true in the constructor will result in a buffer stream that can be JSON.parsed. The array of values is stored in the data property. Example of default JSON buffer:

{
  "data": [0, 100, 200, ..., 400]
}

The property name and other fields can be customized by providing a head or tail configuration to overwrite the defaults for JSON.

Testing

npm test

License

MIT License, Copyright (c) 2015 Jordan Santell