//創(chuàng)建一個(gè)音頻上下文、考慮兼容性問題
 let audioCtx = new (window.AudioContext || window.webkitAudioContext)();
 //添加一個(gè)音頻源節(jié)點(diǎn)
 let source = audioCtx.createBufferSource();
//res.arrayBuffer是將數(shù)據(jù)轉(zhuǎn)換為arrayBuffer格式
 fetch(url).then((res) => res.arrayBuffer()).then((res) => {
        //decodeAudioData是將arrayBuffer格式數(shù)據(jù)轉(zhuǎn)換為audioBuffer
        audioCtx.decodeAudioData(res).then((buffer) => {
          // decodeAudioData解碼完成后，返回一個(gè)AudioBuffer對(duì)象
          // 繪制音頻波形圖
          draw(buffer);
          // 連接音頻源
          source.buffer = buffer;
          source.connect(audioCtx.destination);
          // 音頻數(shù)據(jù)處理完畢
        });
      });

function draw(buffer) {
  // buffer.numberOfChannels返回音頻的通道數(shù)量，1即為單聲道，2代表雙聲道。這里我們只取一條通道的數(shù)據(jù)
  let data = [];
  let originData = buffer.getChannelData(0);
  // 存儲(chǔ)所有的正數(shù)據(jù)
  let positives = [];
  // 存儲(chǔ)所有的負(fù)數(shù)據(jù)
  let negatives = [];
  // 先每隔50條數(shù)據(jù)取1條
  for (let i = 0; i < originData.length; i += 50) {
    data.push(originData[i]);
  }
  // 再?gòu)膁ata中每10條取一個(gè)最大值一個(gè)最小值
  for (let j = 0, len = data.length / 10; j < len; j++) {
    let temp = data.slice(j * 10, (j + 1) * 10);
    positives.push(Math.max(...temp));
    negatives.push(Math.min(...temp));
  }
  if (canvas.getContext) {
    let ctx = canvas.getContext("2d");
    canvas.width = positives.length;
    let x = 0;
    let y = 75;
    let offset = 0;
    var grd = ctx.createLinearGradient(0, 0, canvas.width, 0);
    // 為漸變添加顏色，參數(shù)1表示漸變開始和結(jié)束之間的位置（用0至1的占比表示），參數(shù)2位顏色
    grd.addColorStop(0, "yellow");
    grd.addColorStop(0.5, "red");
    grd.addColorStop(1, "blue");
    ctx.fillStyle = grd;
    ctx.beginPath();
    ctx.moveTo(x, y);
    // 橫坐標(biāo)上方繪制正數(shù)據(jù)，下方繪制負(fù)數(shù)據(jù)
    // 先從左往右繪制正數(shù)據(jù)
    // x + 0.5是為了解決canvas 1像素線條模糊的問題
    for (let k = 0; k < positives.length; k++) {
      ctx.lineTo(x + k + 0.5, y - 50 * positives[k]);
    }
    // 再?gòu)挠彝罄L制負(fù)數(shù)據(jù)
    for (let l = negatives.length - 1; l >= 0; l--) {
      ctx.lineTo(x + l + 0.5, y + 50 * Math.abs(negatives[l]));
    }
    // 填充圖形
    ctx.fill();
  }
}

    const audio =document.querySelector('audio')
    //解決音頻跨域問題
    audio.crossOrigin ='anonymous'
    const  canvas =document.querySelector('canvas')
    const ctx=canvas.getContext("2d")
        function initCanvas(){
        //初始化canvas
            canvas.width=window.innerWidth*devicePixelRatio
            canvas.height=(window.innerHeight/2)*devicePixelRatio
        }
        initCanvas()
        //將數(shù)據(jù)提出來(lái)
        let dataArray,analyser;
        //播放事件
        audio.onplay=function(){
            //創(chuàng)建一個(gè)音頻上下文實(shí)例
            const audioCtx=new (window.AudioContext || window.webkitAudioContext)();
            //添加一個(gè)音頻源節(jié)點(diǎn)
            const source=audioCtx.createMediaElementSource(audio);
            //分析器節(jié)點(diǎn)
             analyser=audioCtx.createAnalyser();
            //fft分析器  越大 分析越細(xì)
            analyser.fftSize=512
            //創(chuàng)建一個(gè)無(wú)符號(hào)字節(jié)的數(shù)組
             dataArray=new Uint8Array( analyser.frequencyBinCount);
            //音頻源節(jié)點(diǎn) 鏈接分析器
            source.connect(analyser)
            //分析器鏈接輸出設(shè)備
            analyser.connect(audioCtx.destination,)
        }

            requestAnimationFrame(draw)
            //
            const {width ,height}=canvas;
            ctx.clearRect(0,0,width,height)
            //分析器節(jié)點(diǎn)分析出的數(shù)據(jù)到數(shù)組中
            ctx.fillStyle='#78C5F7'
           ctx.lineWidth = 2;
            ctx.beginPath();
            //getByteFrequencyData，分析當(dāng)前音頻源的數(shù)據(jù) 裝到dataArray數(shù)組中去
            //獲取實(shí)時(shí)數(shù)據(jù)
            analyser.getByteFrequencyData(dataArray)
            // console.log(dataArray);
            const len =dataArray.length;
            const barWidth=width/len;
            let x=0;
            for(let i=0;i<len;i++){
                const data=dataArray[i];
                const barHeight=data/255*height;
                // ctx.fillRect(x,y,barWidth,height)
        let v = dataArray[i] / 128.0;
        let y = v * height/2;
        if(i === 0) {
            ctx.moveTo(x, y);
        } else {
            ctx.lineTo(x, y);
        }
        x += barWidth;
            }
            // ctx.lineTo(canvas.width, canvas.height/2);
            ctx.stroke();
        }
        draw();

   audio.crossOrigin ='anonymous'