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- self.onmessage = function (e) {
- transAudioData.transcode(e.data)
- }
- let transAudioData = {
- transcode (audioData) {
- let output = transAudioData.to16kHz(audioData)
- output = transAudioData.to16BitPCM(output)
- output = Array.from(new Uint8Array(output.buffer))
- self.postMessage(output)
- // return output
- },
- to16kHz (audioData) {
- // console.log('to16kHzto16kHz pre', JSON.stringify(audioData))
- const data = new Float32Array(audioData)
- const fitCount = Math.round(data.length * (16000 / 44100))
- const newData = new Float32Array(fitCount)
- const springFactor = (data.length - 1) / (fitCount - 1)
- newData[0] = data[0]
- for (let i = 1; i < fitCount - 1; i++) {
- const tmp = i * springFactor
- const before = Math.floor(tmp).toFixed()
- const after = Math.ceil(tmp).toFixed()
- const atPoint = tmp - before
- newData[i] = data[before] + (data[after] - data[before]) * atPoint
- }
- newData[fitCount - 1] = data[data.length - 1]
- // console.log('to16kHzto16kHz after', JSON.stringify(newData))
- return newData
- },
- to16BitPCM (input) {
- const dataLength = input.length * (16 / 8)
- const dataBuffer = new ArrayBuffer(dataLength)
- const dataView = new DataView(dataBuffer)
- let offset = 0
- for (let i = 0; i < input.length; i++, offset += 2) {
- const s = Math.max(-1, Math.min(1, input[i]))
- dataView.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7fff, true)
- }
- return dataView
- }
- }
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