奋斗的宽

01async function getWebFileArrayBuffer(url) {
02  return await fetch(url).then(response => response.arrayBuffer())
03}
04
05async function getWebPcm2WavArrayBuffer(url) {
06  const bytes = await getWebFileArrayBuffer(url)
07  return addWavHeader(bytes, 16000, 16, 1) // 这里是当前业务需求，特定的参数，采样率16000，采样位数16，声道数1
08}
09
10function addWavHeader(samples, sampleRateTmp, sampleBits, channelCount) {
11  let dataLength = samples.byteLength
12  /* 新的buffer类，预留 44 bytes 的heaer 空间 */
13  let buffer = new ArrayBuffer(44 + dataLength)
14  /* 转为 Dataview, 利用 API 来填充字节 */
15  let view = new DataView(buffer)
16  /* 定义一个内部函数，以 big end 数据格式填充字符串至 DataView */
17  function writeString(view, offset, string) {
18    for (let i = 0; i < string.length; i++) {
19      view.setUint8(offset + i, string.charCodeAt(i))
20    }
21  }
22
23  let offset = 0
24  /* ChunkID, 4 bytes,  资源交换文件标识符 */
25  writeString(view, offset, 'RIFF')
26  offset += 4
27  /* ChunkSize, 4 bytes, 下个地址开始到文件尾总字节数,即文件大小-8 */
28  view.setUint32(offset, /* 32 */ 36 + dataLength, true)
29  offset += 4
30  /* Format, 4 bytes, WAV文件标志 */
31  writeString(view, offset, 'WAVE')
32  offset += 4
33  /* Subchunk1 ID, 4 bytes, 波形格式标志 */
34  writeString(view, offset, 'fmt ')
35  offset += 4
36  /* Subchunk1 Size, 4 bytes, 过滤字节,一般为 0x10 = 16 */
37  view.setUint32(offset, 16, true)
38  offset += 4
39  /* Audio Format, 2 bytes, 格式类别 (PCM形式采样数据) */
40  view.setUint16(offset, 1, true)
41  offset += 2
42  /* Num Channels, 2 bytes,  通道数 */
43  view.setUint16(offset, channelCount, true)
44  offset += 2
45  /* SampleRate, 4 bytes, 采样率,每秒样本数,表示每个通道的播放速度 */
46  view.setUint32(offset, sampleRateTmp, true)
47  offset += 4
48  /* ByteRate, 4 bytes, 波形数据传输率 (每秒平均字节数) 通道数×每秒数据位数×每样本数据位/8 */
49  view.setUint32(offset, sampleRateTmp * channelCount * (sampleBits / 8), true)
50  offset += 4
51  /* BlockAlign, 2 bytes, 快数据调整数 采样一次占用字节数 通道数×每样本的数据位数/8 */
52  view.setUint16(offset, channelCount * (sampleBits / 8), true)
53  offset += 2
54  /* BitsPerSample, 2 bytes, 每样本数据位数 */
55  view.setUint16(offset, sampleBits, true)
56  offset += 2
57  /* Subchunk2 ID, 4 bytes, 数据标识符 */
58  writeString(view, offset, 'data')
59  offset += 4
60  /* Subchunk2 Size, 4 bytes, 采样数据总数,即数据总大小-44 */
61  view.setUint32(offset, dataLength, true)
62  offset += 4
63
64  /* 数据流需要以大端的方式存储，定义不同采样比特的 API */
65  function floatTo32BitPCM(output, offset, input) {
66    input = new Int32Array(input)
67    for (let i = 0; i < input.length; i++, offset += 4) {
68      output.setInt32(offset, input[i], true)
69    }
70  }
71  function floatTo16BitPCM(output, offset, input) {
72    input = new Int16Array(input)
73    for (let i = 0; i < input.length; i++, offset += 2) {
74      output.setInt16(offset, input[i], true)
75    }
76  }
77  function floatTo8BitPCM(output, offset, input) {
78    input = new Int8Array(input)
79    for (let i = 0; i < input.length; i++, offset++) {
80      output.setInt8(offset, input[i], true)
81    }
82  }
83  if (sampleBits == 16) {
84    floatTo16BitPCM(view, 44, samples)
85  } else if (sampleBits == 8) {
86    floatTo8BitPCM(view, 44, samples)
87  } else {
88    floatTo32BitPCM(view, 44, samples)
89  }
90  return view.buffer
91}
92
93export default async function getWebPcm2WavBase64(url) {
94  let bytes = await getWebPcm2WavArrayBuffer(url)
95  return `data:audio/wav;base64,${btoa(
96    new Uint8Array(bytes).reduce((data, byte) => {
97      return data + String.fromCharCode(byte)
98    }, '')
99  )}`
100}
101