无需再次下载即可克隆音频源

Question

I'm creating a piano in the browser using javascript. In order for me to play the same key multiple times simultaneously, instead of just playing the Audio object, I clone it and play the clone, otherwise I'd have to wait for the audio to finish or to restart it, which I don't want.

I've done something like this:

var audioSrc = new Audio('path/');
window.onkeypress = function(event) {
    var currentAudioSrc = audioSrc.cloneNode();
    currentAudioSrc.play();
}

The problem is, I was checking chrome's inspector, and I noticed that every time I clone the object, the browser download it again

I checked some people who wanted to achieve similar things, and noticed that most of them have the same problem that I do, they redownload the file. The only example I found that can play the same audio source multiple times simultaneously is SoundJs http://www.createjs.com/SoundJS

I tried checking the source could but couldn't figure out how it was done. Any idea?

---

Answer 1

With the webAudioAPI you could do something like that :

• Download once the file via XMLHttpRequest.
• Append the response to a buffer
• Create a new bufferSource and play it on each call
• Fallback to your first implementation if webAudioAPI is not supported (IE)

 window.AudioContext = window.AudioContext||window.webkitAudioContext; if(!window.AudioContext) yourFirstImplementation(); else{ var buffer, ctx = new AudioContext(), gainNode = ctx.createGain(); gainNode.connect(ctx.destination); var vol = document.querySelector('input'); vol.value = gainNode.gain.value; vol.addEventListener('change', function(){ gainNode.gain.value = this.value; }, false); function createBuffer(){ ctx.decodeAudioData(this.response, function(b) { buffer = b; }, function(e){console.warn(e)}); var button = document.querySelector('button'); button.addEventListener('click', function(){playSound(buffer)}); button.className = 'ready'; } var file = 'https://dl.dropboxusercontent.com/s/agepbh2agnduknz/camera.mp3', xhr = new XMLHttpRequest(); xhr.onload = createBuffer; xhr.open('GET', file, true); xhr.responseType = 'arraybuffer'; xhr.send(); function playSound(buf){ var source = ctx.createBufferSource(); source.buffer = buf; source.connect(gainNode); source.onended = function(){if(this.stop)this.stop(); if(this.disconnect)this.disconnect();} source.start(0); } } function yourFirstImplementation(){ alert('webAudioAPI is not supported by your browser'); }

 button{opacity: .2;} button.ready{opacity: 1};

 <button>play</button> <input type="range" max="5" step=".01" title="volume"/>

Answer 2

cloneNode have one boolean argument:

var dupNode = node.cloneNode(deep);
/*
  node
    The node to be cloned.
  dupNode
    The new node that will be a clone of node
  deep(Optional)
     true if the children of the node should also be cloned, or false to clone only the specified node.
*/

Also note fromMDN :

Deep is an optional argument. If omitted, the method acts as if the value of deep was true, defaulting to using deep cloning as the default behavior. To create a shallow clone, deep must be set to false.

This behavior has been changed in the latest spec, and if omitted, the method will act as if the value of deep was false. Though It's still optional, you should always provide the deep argument both for backward and forward compatibility

So, try to use deep = false to prevent download resource:

var audioSrc = new Audio('path/');
window.onkeypress = function(event) {
    var currentAudioSrc = audioSrc.cloneNode(false);
    currentAudioSrc.play();
}

Answer 3

Load it manually and assign a Blob URL of the binary data to src :

<audio id="audioEl" data-src="audio.mp3"></audio>

var xhr = new XMLHttpRequest();
xhr.open('GET', audioEl.dataset.src);
xhr.responseType = 'blob';
xhr.onload = () => {
    audioEl.src = URL.createObjectURL(xhr.response);
};
xhr.send();

This way when you clone it, only the reference to the in-memory binary data is cloned.