@voice-ping/cognitive-services-speech/distrib/es2015/src/common/RiffPcmEncoder.js

VoicePing Cognitive Services Speech SDK for JavaScript forked from Microsoft

// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT license.
export class RiffPcmEncoder {
    constructor(actualSampleRate, desiredSampleRate) {
        this.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;
        };
        this.setString = (view, offset, str) => {
            for (let i = 0; i < str.length; i++) {
                view.setUint8(offset + i, str.charCodeAt(i));
            }
        };
        this.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);
            }
        };
        this.downSampleAudioFrame = (srcFrame, srcRate, dstRate) => {
            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;
        };
        this.privActualSampleRate = actualSampleRate;
        this.privDesiredSampleRate = desiredSampleRate;
    }
}

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