js audio音频剪裁 JS实现audio音频剪裁剪切复制播放与上传(步骤详解)

file.onchange = function (event) {
 var file = event.target.files[0];
 // 开始识别
 var reader = new FileReader();
 reader.onload = function (event) {
 var arrBuffer = event.target.result;
 // arrBuffer就是包含音频数据的ArrayBuffer对象
 });
 reader.readAsArrayBuffer(file);
};

var audioCtx = new AudioContext();

audioCtx.decodeAudioData(arrBuffer, function(audioBuffer) {
 // audioBuffer就是AudioBuffer
});

duration
numberOfChannels
sampleRate

getChannelData()
copyFromChannel()
copyToChannel()

// 声道数量和采样率
var channels = audioBuffer.numberOfChannels;
var rate = audioBuffer.sampleRate;

// 截取前3秒
var startOffset = 0;
var endOffset = rate * 3;
// 3秒对应的帧数
var frameCount = endOffset - startOffset;

// 创建同样采用率、同样声道数量，长度是前3秒的空的AudioBuffer
var newAudioBuffer = new AudioContext().createBuffer(channels, endOffset - startOffset, rate);
// 创建临时的Array存放复制的buffer数据
var anotherArray = new Float32Array(frameCount);
// 声道的数据的复制和写入
var offset = 0;
for (var channel = 0; channel < channels; channel++) {
 audioBuffer.copyFromChannel(anotherArray, channel, startOffset);
 newAudioBuffer.copyToChannel(anotherArray, channel, offset);
}

// newAudioBuffer就是全新的复制的3秒长度的AudioBuffer对象

// 创建AudioBufferSourceNode对象
var source = audioCtx.createBufferSource();
// 设置AudioBufferSourceNode对象的buffer为复制的3秒AudioBuffer对象
source.buffer = newAudioBuffer;
// 这一句是必须的，表示结束，没有这一句没法播放，没有声音
// 这里直接结束，实际上可以对结束做一些特效处理
source.connect(audioCtx.destination);
// 资源开始播放
source.start();

// Convert AudioBuffer to a Blob using WAVE representation
function bufferToWave(abuffer, len) {
 var numOfChan = abuffer.numberOfChannels,
 length = len * numOfChan * 2 + 44,
 buffer = new ArrayBuffer(length),
 view = new DataView(buffer),
 channels = [], i, sample,
 offset = 0,
 pos = 0;

 // write WAVE header
 // "RIFF"
 setUint32(0x46464952);
 // file length - 8   
 setUint32(length - 8);
 // "WAVE"   
 setUint32(0x45564157);
 // "fmt " chunk
 setUint32(0x20746d66); 
 // length = 16   
 setUint32(16); 
 // PCM (uncompressed)    
 setUint16(1); 
 setUint16(numOfChan);
 setUint32(abuffer.sampleRate);
 // avg. bytes/sec
 setUint32(abuffer.sampleRate * 2 * numOfChan);
 // block-align
 setUint16(numOfChan * 2);
 // 16-bit (hardcoded in this demo)
 setUint16(16);    
 // "data" - chunk
 setUint32(0x61746164); 
 // chunk length   
 setUint32(length - pos - 4);   

 // write interleaved data
 for(i = 0; i < abuffer.numberOfChannels; i++)
 channels.push(abuffer.getChannelData(i));

 while(pos < length) {
  // interleave channels
 for(i = 0; i < numOfChan; i++) {
  // clamp
  sample = Math.max(-1, Math.min(1, channels[i][offset])); 
  // scale to 16-bit signed int
  sample = (0.5 + sample < 0 ? sample * 32768 : sample * 32767)|0; 
  // write 16-bit sample
  view.setInt16(pos, sample, true);  
  pos += 2;
 }
 // next source sample
 offset++     
 }

 // create Blob
 return new Blob([buffer], {type: "audio/wav"});

 function setUint16(data) {
 view.setUint16(pos, data, true);
 pos += 2;
 }

 function setUint32(data) {
 view.setUint32(pos, data, true);
 pos += 4;
 }
}

var blob = bufferToWave(newAudioBuffer, frameCount);

<audio id="audio" controls=""></audio>

audio.src = URL.createObjectURL(blob);

var reader2 = new FileReader();
reader2.onload = function(event){
 audio.src = event.target.result;
};
reader2.readAsDataURL(blob);

var formData = new FormData();
formData.append('audio', blob);
// 请求走起
var xhr = new XMLHttpRequest();
xhr.open('POST', this.cgiGetImg, true);
// 请求成功
xhr.onload = function () {
};
// 发送数据
xhr.send(formData);