transcode.worker.js 1.5 KB

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  1. self.onmessage = function (e) {
  2. transAudioData.transcode(e.data)
  3. }
  4. let transAudioData = {
  5. transcode (audioData) {
  6. let output = transAudioData.to16kHz(audioData)
  7. output = transAudioData.to16BitPCM(output)
  8. output = Array.from(new Uint8Array(output.buffer))
  9. self.postMessage(output)
  10. // return output
  11. },
  12. to16kHz (audioData) {
  13. // console.log('to16kHzto16kHz pre', JSON.stringify(audioData))
  14. const data = new Float32Array(audioData)
  15. const fitCount = Math.round(data.length * (16000 / 44100))
  16. const newData = new Float32Array(fitCount)
  17. const springFactor = (data.length - 1) / (fitCount - 1)
  18. newData[0] = data[0]
  19. for (let i = 1; i < fitCount - 1; i++) {
  20. const tmp = i * springFactor
  21. const before = Math.floor(tmp).toFixed()
  22. const after = Math.ceil(tmp).toFixed()
  23. const atPoint = tmp - before
  24. newData[i] = data[before] + (data[after] - data[before]) * atPoint
  25. }
  26. newData[fitCount - 1] = data[data.length - 1]
  27. // console.log('to16kHzto16kHz after', JSON.stringify(newData))
  28. return newData
  29. },
  30. to16BitPCM (input) {
  31. const dataLength = input.length * (16 / 8)
  32. const dataBuffer = new ArrayBuffer(dataLength)
  33. const dataView = new DataView(dataBuffer)
  34. let offset = 0
  35. for (let i = 0; i < input.length; i++, offset += 2) {
  36. const s = Math.max(-1, Math.min(1, input[i]))
  37. dataView.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7fff, true)
  38. }
  39. return dataView
  40. }
  41. }