使用Javascript SDK将WebAudio数据发布到Soundcloud轨道

Question

I'm trying to use an audio buffer composed of Float32Array s (1 for each channel) as asset data to create a soundcloud track. The audio buffer for a mono recording looks like this:

[Float32Array { 0=-0.0001220703125,  1=0.000579833984375,  2=0.000762939453125,  ...}]

So I assume that I should convert it to a binary string. To know the correct encoding, I took a look at http://connect.soundcloud.com/examples/recording.html It's flash but at the end the following post is done:

audio.wav
--ievejmnijdgyooinchslwnpygpivapif
Content-Disposition: form-data; name="track[asset_data]"; filename="audio.wav"
Content-Type: application/octet-stream

RIFF(WAVEfmt D¬XdataÚÿÇÿÿ+ÿc]ÿ1&»ÿUÿ(1ÊÿEc&môã...

In order to turn my audio buffer into such, I used code similar to https://gist.github.com/kevincennis/9754325 so that now my process looks like:

worker.onmessage = function( e ) {
  var blob = e.data;
  var reader = new window.FileReader();
  reader.onloadend = function() {
     var binaryData = reader.result;                
     SC.post('/tracks', {
       asset_data : binaryData,
       title : 'recording'
     });
  };
  reader.readAsText(blob);
});

Still, there should be some problem with the encoding. The above, produces the following post:

_status_code_map[302]   200
asset_data              RIFF ���WAVEfmt �����D�������data����
format                  json
oauth_token             1....
title                   recording

but the response of Soundclound API is still: "NetworkError: 422 Unprocessable Entity - https://api.soundcloud.com/tracks "

Can anybody spot what's wrong?

Answer 1

Turns out that Soundcloud only accept the request if it's in multipart form encoding. It seems not possible to me to achieve this using the SDK. This is the code using angular.js:

worker.onmessage = function( e ) {
  var blob = e.data;
  var fd = new FormData();
  fd.append('oauth_token', SC.accessToken());
  fd.append('format','json');
  fd.append('track[title]', 'recording');
  fd.append('track[asset_data]', blob);

  $http.post('https://api.soundcloud.com/tracks', fd, {
    transformRequest: angular.identity,
    headers: {'Content-Type': undefined}
  })
});