node-alsa
ALSA bindings for Node.js
Requirements
You must have a system on which ALSA is supported with the libasound2-dev package installed:
$ sudo apt-get install libasound2-devYou'll also probably want to have an audio device for either playback or capture.
Installation
Install with npm:
$ npm install alsaor via git:
$ npm install git+https://github.com/xdissent/node-alsa.gitUsage
The alsa module exports 2 high-level classes for playback and recording.
var alsa = // The following variables represent the defaults for the Playback and Capture constructors. device = 'default' // ALSA default device channels = 2 // Stereo rate = 44100 // Sample rate format = alsaFORMAT_S16_LE // PCM format (signed 16 bit LE int) access = alsaACCESS_RW_INTERLEAVED // Access mode latency = 500; // Desired latency in milliseconds // The Capture class is a stream.Readable subclass.var capture = device channels rate format access latency;capture; // Treat it like any other readable stream. // The Playback class is a stream.Writable subclass.var playback = device channels rate format access latency;processstdin; // Treat it like any other writable stream. // Want to do both at the same time? Not a problem:capture; // Of course, your sound hardware might say otherwise.Examples
Downsample audio captured from an ALSA device to a sample rate of 11025, in mono, encoded to 32 bit float PCM data and output to stdout:
alsa = require 'alsa'stream = require 'stream' : -> streamTransformcall this # Naively drop 3 out of 4 samples, combine the interleaved left and right into # a single sample, then convert to 32 bit float PCM data. : # This is the naive part. Should be checking for partial samples. floats = chunklength / 4 f = 0 for i in 0...chunklengthby 16 # 4 bytes per frame downsampled by 4. l16 = chunkreadInt16LE i # Read left channel sample. r16 = chunkreadInt16LE i + 2 # Read right channel sample. # Sum samples and normalize as a float floatswriteFloatLE l16 + r16 / 65536f f += 4 # Skip ahead 4 bytes in buffer (32 bit float). @push floats # Write transformed samples to stream... callback # And we're done. # Create a Capture and a Downer and chain them to stdout. capture = downer = capturepipedownerpipeprocessstdout