How can I load only waveform and wait to user click 'play' to download the audio on Wavesurfer-js?

On my server I use Audiowaveform to generate JSON data from my audio files.

On frontend I use Wavesurfer-JS to draw the waveform based on previous JSON data.

The problem is that on page ready the Wavesurfer-JS download on background the audio file all the time (and not only when the user hit the play button).

This is my try.

This is the salient part:

<div id="waveform">
    <audio id="song" style="display: none" preload="false" src="http://api.soundcloud.com/tracks/45398925/stream?client_id=fa791b761f68cafa375ab5f7ea51927a"></audio>
</div>

<script>
    var wavesurfer = WaveSurfer.create({
      container: '#waveform',
      waveColor: 'grey',
      backend: 'MediaElement',
      mediaType:'audio',
      progressColor: 'red',
      cursorColor: '#fff',
      normalize: true,
      barWidth: 3
    });

    wavesurfer.load(document.querySelector('#song'), ['.$json.']);
</script>

So basically I need to focus on wavesurfer.load and add a new function to this Javascript to only draw from peaks(JSON data) the waveform and don't download audio file on page load but only when the user hit the play button.

How can I achieve it?

Solution

Took me a while to hack around the wavesurfer js code to find out how I can make it draw without loading the song already :P

Setting the peaks in the backend variable and calling drawBuffer did the trick, combining that with some play button logic and we get the following code:

//Create new wavesurfer
wavesurfer = WaveSurfer.create({
    container: '#waveform',
    backend: 'MediaElement',
    mediaType:'audio',
    normalize: true,
    barWidth: 3
});

//Set song
wavesurfer.song = "http://www.stephaniequinn.com/Music/Allegro%20from%20Duet%20in%20C%20Major.mp3"

//Set peaks
wavesurfer.backend.peaks = [0.0218, 0.0183, 0.0165, 0.0198, 0.2137, 0.2888, 0.2313, 0.15, 0.2542, 0.2538, 0.2358, 0.1195, 0.1591, 0.2599, 0.2742, 0.1447, 0.2328, 0.1878, 0.1988, 0.1645, 0.1218, 0.2005, 0.2828, 0.2051, 0.1664, 0.1181, 0.1621, 0.2966, 0.189, 0.246, 0.2445, 0.1621, 0.1618, 0.189, 0.2354, 0.1561, 0.1638, 0.2799, 0.0923, 0.1659, 0.1675, 0.1268, 0.0984, 0.0997, 0.1248, 0.1495, 0.1431, 0.1236, 0.1755, 0.1183, 0.1349, 0.1018, 0.1109, 0.1833, 0.1813, 0.1422, 0.0961, 0.1191, 0.0791, 0.0631, 0.0315, 0.0157, 0.0166, 0.0108];

//Draw peaks
wavesurfer.drawBuffer();

//Variable to check if song is loaded
wavesurfer.loaded = false;

//Load song when play is pressed
wavesurfer.on("play", function () {
    if(!wavesurfer.loaded) {
        wavesurfer.load(wavesurfer.song, wavesurfer.backend.peaks);
    }
});

//Start playing after song is loaded
wavesurfer.on("ready", function () {
    if(!wavesurfer.loaded) {
        wavesurfer.loaded = true;
        wavesurfer.play();
    }
});

Make sure to remove the unnecessary<audio> tag from the html, browsers seem to download all audio files in those tags on load and attributes like preload=false seem to be ignored...