45 lines
1.4 KiB
JavaScript
45 lines
1.4 KiB
JavaScript
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;(function () {
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let self = this
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self.onmessage = function (e) {
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transAudioData.transcode(e.data)
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}
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let transAudioData = {
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transcode(audioData) {
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let output = transAudioData.to16kHz(audioData)
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output = transAudioData.to16BitPCM(output)
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output = Array.from(new Uint8Array(output.buffer))
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self.postMessage(output)
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// return output
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},
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to16kHz(audioData) {
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var data = new Float32Array(audioData)
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var fitCount = Math.round(data.length * (16000 / 44100))
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var newData = new Float32Array(fitCount)
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var springFactor = (data.length - 1) / (fitCount - 1)
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newData[0] = data[0]
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for (let i = 1; i < fitCount - 1; i++) {
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var tmp = i * springFactor
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var before = Math.floor(tmp).toFixed()
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var after = Math.ceil(tmp).toFixed()
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var atPoint = tmp - before
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newData[i] = data[before] + (data[after] - data[before]) * atPoint
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}
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newData[fitCount - 1] = data[data.length - 1]
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return newData
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},
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to16BitPCM(input) {
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var dataLength = input.length * (16 / 8)
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var dataBuffer = new ArrayBuffer(dataLength)
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var dataView = new DataView(dataBuffer)
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var offset = 0
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for (var i = 0; i < input.length; i++, offset += 2) {
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var s = Math.max(-1, Math.min(1, input[i]))
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dataView.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7fff, true)
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}
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return dataView
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}
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}
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})();
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