This is a ffmpeg wrapper that will take in multiple audio files and combines them into a single file. Silent gaps will be put between the parts so that every new part starts from full second and there is at least 1 second pause between every part. The final file will be exported in mp3, ogg, ac3, m4a and caf(IMA-ADPCM) to support as many devices as possible. This tool will also generate a JSON file that is compatible with SwishSprite.

Purpose

iOS, Windows Phone and some Android phones have very limited HTML5 audio support. They only support playing single file at a time and loading in new files requires user interaction and has a big latency. To overcome this there is a technique to combine all audio into single file and only play/loop certain parts of that file.

Installation

npm install -g audiosprite

Hints for Windows users

• You need to install Node.js
• Use Git Bash instead of Command Line or Powershell
• Download ffmpeg and include it in your path export PATH=$PATH:path/to/ffmpeg/bin
• IMA-ADPCM(the fastest iPhone format) will only be generated if you are using OSX.

Usage

> audiosprite --help
info: Usage: audiosprite [options] file1.mp3 file2.mp3 *.wav
info: Options:
  --output, -o      Name for the output file.                                    [default: "output"]
  --priority, -y    The JSON list of audio aliases by priority.                  [default: ""]
  --export, -e      Limit exported file types. Comma separated extension list.   [default: ""]
  --log, -l         Log level (debug, info, notice, warning, error).             [default: "info"]
  --autoplay, -a    Autoplay sprite name                                         [default: null]
  --silence, -s     Add special "silence" track with specified duration.         [default: 0]
  --samplerate, -r  Sample rate.                                                 [default: 44100]
  --channels, -c    Number of channels (1=mono, 2=stereo).                       [default: 1]
  --rawparts, -p    Include raw slices(for Web Audio API) in specified formats.  [default: ""]
  --bitrate, -b     The bitrate quality for the exported audio.                  [default: 128]
  --help, -h        Show this help message.


> audiosprite --autoplay bg_loop --output mygameaudio bg_loop.wav *.mp3
info: File added OK file=bg_loop.wav
info: 1.25s silence gap added OK
info: File added OK file=click.mp3
info: 1.70s silence gap added OK
info: Exported caf OK file=mygameaudio.caf
info: Exported ac3 OK file=mygameaudio.ac3
info: Exported mp3 OK file=mygameaudio.mp3
info: Exported m4a OK file=mygameaudio.m4a
info: Exported ogg OK file=mygameaudio.ogg
info: Exported json OK file=mygameaudio.json
info: All done


> cat mygameaudio.json
{
  "resources": [
    "mygameaudio.caf",
    "mygameaudio.ac3",
    "mygameaudio.mp3",
    "mygameaudio.m4a",
    "mygameaudio.ogg"
  ],
  "spritemap": {
    "bg_loop": {
      "start": 0,
      "end": 3.75,
      "loop": true,
      "priority": 0
    },
    "click": {
      "start": 5,
      "end": 5.3,
      "loop": false,
      "priority": 0
    }
  },
  "autoplay": "bg_loop"
}

Setting autoplay track

You can use --autoplay option to set a track that will start playing automatically. This track is then marked as autoplay and looping in the JSON. This syntax is Jukebox framework specific.

Custom silent track

On some cases starting and pausing a file has bigger latency than just setting playhead position. You may get better results if your file is always playing. --silence <duration> option will generate extra track named silence that you can play instead of pausing the file.

Usage with Swish Sprite

Generated JSON file can be passed straight into cloudkid.SwishSprite constructor. Check out Swish Sprite documentation more info.

// Load the audiosprite map JSON with jQuery
$.getJSON("sprite.json", function(data){

	// Create new SwishSprite from map
	var audio = new cloudkid.SwishSprite(data);
	
	
	// Trigger a user load on a button press
	// for mobile browser that require a user's
	// input before initiating the audio load
	$('button#load').click(function(){
		audio.load();
	});
	
	// Add event for when audio finishes loading
	audio.on('loaded', function(){
		audio.play('bg_loop');
	});
});