bufferToWave.js

/* https://www.russellgood.com/how-to-convert-audiobuffer-to-audio-file/ */

export function bufferToWave (abuffer, len) {
var numOfChan = abuffer.numberOfChannels,
length = len * numOfChan * 2 + 44,
buffer = new ArrayBuffer(length),
view = new DataView(buffer),
channels = [], i, sample,
offset = 0,
pos = 0;

// write WAVE header
setUint32(0x46464952);                         // "RIFF"
setUint32(length - 8);                         // file length - 8
setUint32(0x45564157);                         // "WAVE"

setUint32(0x20746d66);                         // "fmt " chunk
setUint32(16);                                 // length = 16
setUint16(1);                                  // PCM (uncompressed)
setUint16(numOfChan);
setUint32(abuffer.sampleRate);
setUint32(abuffer.sampleRate * 2 * numOfChan); // avg. bytes/sec
setUint16(numOfChan * 2);                      // block-align
setUint16(16);                                 // 16-bit (hardcoded in this demo)

setUint32(0x61746164);                         // "data" - chunk
setUint32(length - pos - 4);                   // chunk length

// write interleaved data
for(i = 0; i < abuffer.numberOfChannels; i++)
channels.push(abuffer.getChannelData(i));

while(pos < length) {
for(i = 0; i < numOfChan; i++) {             // interleave channels
sample = Math.max(-1, Math.min(1, channels[i][offset])); // clamp
sample = (0.5 + sample < 0 ? sample * 32768 : sample * 32767)|0; // scale to 16-bit signed int
view.setInt16(pos, sample, true);          // write 16-bit sample
pos += 2;
}
offset++                                     // next source sample
}

// create Blob
return new Blob([buffer], {type: "audio/wav"});

function setUint16(data) {
view.setUint16(pos, data, true);
pos += 2;
}

function setUint32(data) {
view.setUint32(pos, data, true);
pos += 4;
}
} // bufferToWave