stopPreview() {
if (this.source) {
this.source.disconnect(this.waveformView)
this.source.stop()
this.source = null
if (this.canvas) {
let context = this.canvas.getContext('2d')
let {width, height} = this.canvas
context.clearRect(0, 0, width, height)
}
}
}
startPreview(device) {
this.source = new DeviceSource({audio: {device}})
this.source.connect(this.waveformView)
this.source.promise.catch(console.error)
}