initCamera () { // 初始化摄像头
  this.theVideo = document.getElementById('video')
  let _this = this
     navigator.mediaDevices.getUserMedia({video: true}).then(function (mediaStream) {
        window.stream = mediaStream
        _this.theVideo.srcObject = mediaStream
        _this.theVideo.play()
      })
      navigator.getUserMedia = navigator.getUserMedia ||
        navigator.webkitGetUserMedia ||
        navigator.mozGetUserMedia
      if (navigator.getUserMedia) {
      } else {
        console.log('getUserMedia not supported')
      }
}
pcCameraUpload (index) { // 将获取视频绘制在画布上
      console.log('pcCameraUpload', index)
      let canvas = document.createElement('canvas')
      canvas.width = this.theVideo.videoWidth
      canvas.height = this.theVideo.videoHeight
      let cxt = canvas.getContext('2d')
      cxt.drawImage(this.theVideo, 0, 0, canvas.width, canvas.height)
      this.aCanvasBase = canvas.toDataURL('image/jpeg')
}