File size: 1,496 Bytes
ded73f2 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 | /**
* Encode a decoded AudioBuffer as a 16-bit PCM mono WAV Blob.
* Used at upload/record time so the server (libsndfile) can always decode it.
*/
export function encodeWav(buf: AudioBuffer): Blob {
const sr = buf.sampleRate;
const length = buf.length;
const numCh = 1;
// Mix down to mono in float32
const mono = new Float32Array(length);
const ch0 = buf.getChannelData(0);
if (buf.numberOfChannels === 1) {
mono.set(ch0);
} else {
const ch1 = buf.getChannelData(1);
for (let i = 0; i < length; i++) mono[i] = (ch0[i] + ch1[i]) / 2;
}
// Convert to int16
const dataSize = length * numCh * 2;
const out = new ArrayBuffer(44 + dataSize);
const view = new DataView(out);
let p = 0;
const writeStr = (s: string) => {
for (let i = 0; i < s.length; i++) view.setUint8(p++, s.charCodeAt(i));
};
const writeU32 = (n: number) => {
view.setUint32(p, n, true);
p += 4;
};
const writeU16 = (n: number) => {
view.setUint16(p, n, true);
p += 2;
};
writeStr("RIFF");
writeU32(36 + dataSize);
writeStr("WAVE");
writeStr("fmt ");
writeU32(16);
writeU16(1); // PCM
writeU16(numCh);
writeU32(sr);
writeU32(sr * numCh * 2);
writeU16(numCh * 2);
writeU16(16);
writeStr("data");
writeU32(dataSize);
for (let i = 0; i < length; i++) {
const s = Math.max(-1, Math.min(1, mono[i]));
view.setInt16(44 + i * 2, s < 0 ? s * 0x8000 : s * 0x7fff, true);
}
return new Blob([out], { type: "audio/wav" });
}
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