microsoft-cognitiveservices-speech-sdk
Version:
Microsoft Cognitive Services Speech SDK for JavaScript
61 lines (59 loc) • 2.19 kB
JavaScript
;
// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT license.
Object.defineProperty(exports, "__esModule", { value: true });
exports.RiffPcmEncoder = void 0;
class RiffPcmEncoder {
constructor(actualSampleRate, desiredSampleRate) {
this.privActualSampleRate = actualSampleRate;
this.privDesiredSampleRate = desiredSampleRate;
}
encode(actualAudioFrame) {
const audioFrame = this.downSampleAudioFrame(actualAudioFrame, this.privActualSampleRate, this.privDesiredSampleRate);
if (!audioFrame) {
return null;
}
const audioLength = audioFrame.length * 2;
const buffer = new ArrayBuffer(audioLength);
const view = new DataView(buffer);
this.floatTo16BitPCM(view, 0, audioFrame);
return buffer;
}
setString(view, offset, str) {
for (let i = 0; i < str.length; i++) {
view.setUint8(offset + i, str.charCodeAt(i));
}
}
floatTo16BitPCM(view, offset, input) {
for (let i = 0; i < input.length; i++, offset += 2) {
const s = Math.max(-1, Math.min(1, input[i]));
view.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7FFF, true);
}
}
downSampleAudioFrame(srcFrame, srcRate, dstRate) {
if (!srcFrame) {
return null;
}
if (dstRate === srcRate || dstRate > srcRate) {
return srcFrame;
}
const ratio = srcRate / dstRate;
const dstLength = Math.round(srcFrame.length / ratio);
const dstFrame = new Float32Array(dstLength);
let srcOffset = 0;
let dstOffset = 0;
while (dstOffset < dstLength) {
const nextSrcOffset = Math.round((dstOffset + 1) * ratio);
let accum = 0;
let count = 0;
while (srcOffset < nextSrcOffset && srcOffset < srcFrame.length) {
accum += srcFrame[srcOffset++];
count++;
}
dstFrame[dstOffset++] = accum / count;
}
return dstFrame;
}
}
exports.RiffPcmEncoder = RiffPcmEncoder;
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