soundwave/soundwave.cm

/*
 * soundwave.cm - Standalone audio playback system
 *
 * Creates an audio player instance that manages voices and provides
 * mixed audio output. Platform-agnostic - caller is responsible for
 * feeding the output to the audio device.
 *
 * USAGE:
 *   var soundwave = use('soundwave/soundwave')
 *   var player = soundwave.create({
 *     sample_rate: 44100,
 *     channels: 2,
 *     frames_per_chunk: 1024
 *   })
 *   
 *   // Load and decode audio (caller provides bytes and file path)
 *   var pcm = player.decode(bytes, "mysound.mp3")
 *   
 *   // Play a sound
 *   var voice = player.play(pcm, { loop: true, vol: 0.5 })
 *   voice.stopped = true  // stop it
 *   
 *   // Pull mixed audio frames for output
 *   var blob = player.pull(1024)  // returns stoned blob of f32 stereo samples
 *
 * OBJECTS:
 *
 * Player - Audio player instance
 *   .sample_rate     - output sample rate (default 44100)
 *   .channels        - output channels (default 2)
 *   .frames_per_chunk- default frames per pull (default 1024)
 *   .decode(bytes, path) - decode audio bytes, returns PCM object
 *   .play(pcm, opts) - play a PCM, returns Voice object
 *   .pull(frames)    - pull mixed audio, returns stoned blob
 *   .cleanup()       - remove finished voices
 *
 * PCM - Decoded audio data
 *   .pcm        - stoned blob of f32 stereo samples at player's sample_rate
 *   .channels   - channel count (after conversion)
 *   .sample_rate- sample rate (after conversion)
 *   .frames     - total frames in pcm blob
 *   .path       - source file path
 *
 * Voice - A playing instance of a PCM
 *   .source     - reference to PCM object
 *   .pos        - current frame position (0-indexed)
 *   .vol        - volume 0.0-1.0 (default 1.0)
 *   .loop       - if true, loops when reaching end
 *   .stopped    - set to true to stop playback
 *   .finish_hook- optional callback when voice finishes
 */

var wav = use('wav')
var mp3 = use('mp3')
var flac = use('flac')
var dsp = use('dsp')
var samplerate = use('libsamplerate/convert')
var Blob = use('blob')

var soundwave = {}

var voice = {
  stop() {
    this.stopped = true
  }
}

// Create a new audio player instance
soundwave.create = function(opts) {
  opts = opts || {}
  
  var player = {
    sample_rate: opts.sample_rate || 44100,
    channels: opts.channels || 2,
    frames_per_chunk: opts.frames_per_chunk || 1024,
    voices: [],
    pcm_cache: {}
  }
  
  var BYTES_PER_SAMPLE = 4  // f32
  
  // Normalize decoded audio to player's output format
  function normalize_pcm(decoded, path) {
    var pcm = decoded.pcm
    var channels = decoded.channels || 1
    var rate = decoded.sample_rate || player.sample_rate
    
    // Resample if needed
    if (rate != player.sample_rate) {
      pcm = samplerate.resample(pcm, rate, player.sample_rate, channels)
    }
    
    // Convert mono to stereo if needed
    if (channels == 1 && player.channels == 2) {
      pcm = dsp.mono_to_stereo(pcm)
      channels = 2
    }
    
    // Calculate frames
    var bytes = length(pcm) / 8  // length(blob) is in bits
    var frames = bytes / (player.channels * BYTES_PER_SAMPLE)
    
    return {
      pcm: pcm,
      channels: player.channels,
      sample_rate: player.sample_rate,
      frames: frames,
      path: path
    }
  }
  
  // Decode audio bytes into PCM
  // bytes: blob of encoded audio data
  // path: file path (used to determine format and for caching)
  player.decode = function(bytes, path) {
    if (!bytes || !path) return null
    
    // Check cache
    if (player.pcm_cache[path]) return player.pcm_cache[path]
    
    var decoded = null
    if (ends_with(path, '.wav')) {
      decoded = wav.decode(bytes)
    } else if (ends_with(path, '.mp3')) {
      decoded = mp3.decode(bytes)
    } else if (ends_with(path, '.flac')) {
      decoded = flac.decode(bytes)
    }
    
    if (decoded && decoded.pcm) {
      var normalized = normalize_pcm(decoded, path)
      player.pcm_cache[path] = normalized
      return normalized
    }
    return null
  }
  
  // Pull a chunk of audio from a voice, handling looping
  function pull_voice_chunk(voice, frames) {
    if (voice.stopped) return null
    
    var source = voice.source
    var total_frames = source.frames
    var pos = voice.pos
    var bytes_per_frame = player.channels * BYTES_PER_SAMPLE
    var bits_per_frame = bytes_per_frame * 8
    
    var out = Blob()
    var frames_written = 0
    
    while (frames_written < frames) {
      if (pos >= total_frames) {
        if (voice.loop) {
          pos = 0
        } else {
          break
        }
      }
      
      var frames_available = total_frames - pos
      var frames_needed = frames - frames_written
      var frames_to_read = frames_available < frames_needed ? frames_available : frames_needed
      
      var start_bit = pos * bits_per_frame
      var end_bit = (pos + frames_to_read) * bits_per_frame
      var chunk = source.pcm.read_blob(start_bit, end_bit)
      out.write_blob(chunk)
      
      pos += frames_to_read
      frames_written += frames_to_read
    }
    
    voice.pos = pos
    
    // Pad with silence if needed
    if (frames_written < frames) {
      var silence_frames = frames - frames_written
      var silence = dsp.silence(silence_frames, player.channels)
      out.write_blob(silence)
    }
    
    stone(out)
    return out
  }
  
  // Remove finished voices
  player.cleanup = function() {
    var active = []
    for (var i = 0; i < length(player.voices); i++) {
      var v = player.voices[i]
      var done = v.stopped || (!v.loop && v.pos >= v.source.frames)
      if (!done) {
        push(active, v)
      } else if (v.finish_hook) {
        v.finish_hook()
      }
    }
    player.voices = active
  }
  
  // Play a PCM, returns voice object
  player.play = function(pcm, opts) {
    if (!pcm) return null
    
    var newvoice = meme(voice, {
      source: pcm,
      pos: 0,
      vol: 1.0,
      loop: false,
      stopped: false,
      finish_hook: null
    })
    
    if (opts) {
      if (opts.loop != null) newvoice.loop = opts.loop
      if (opts.vol != null) newvoice.vol = opts.vol
    }
    
    push(player.voices, newvoice)
    return newvoice
  }
  
  // Pull mixed audio frames
  // Returns a stoned blob of f32 samples (channels * frames * 4 bytes)
  player.pull = function(frames) {
    frames = frames || player.frames_per_chunk
    
    var blobs = []
    var vols = []
    
    for (var i = 0; i < length(player.voices); i++) {
      var v = player.voices[i]
      if (v.stopped) continue
      var chunk = pull_voice_chunk(v, frames)
      if (chunk) {
        push(blobs, chunk)
        push(vols, v.vol)
      }
    }
    
    var mixed
    if (length(blobs) == 0) {
      mixed = dsp.silence(frames, player.channels)
    } else {
      mixed = dsp.mix_blobs(blobs, vols)
    }
    
    player.cleanup()
    return mixed
  }
  
  // Convenience: get number of active voices
  player.voice_count = function() {
    return length(player.voices)
  }
  
  return player
}

return soundwave