用randerjs截取视频第一帧时，安卓没啥问题，ios只要一打开autoplay：true就自己弹出来播放视频了

用randerjs截取视频第一帧时，安卓没啥问题，ios只要一打开autoplay：true就自己弹出来播放视频了，不打开autoplay的话截出来是个白色空白

  let video = document.createElement('video')  
  video.muted = true  
  video.autoplay = false  
  video.setAttribute('width', res.width)  
  video.setAttribute('height', res.height)  
  video.setAttribute('preload', 'auto')  
  video.setAttribute('crossOrigin', 'anonymous')   
  video.setAttribute('src', res.filePath)  
  video.addEventListener('loadeddata', function() {  
    let canvas = document.createElement('canvas')  
    let width = video.width  
    let height = video.height  
    canvas.width = width  
    canvas.height = height  
    canvas.getContext('2d').drawImage(video, 0, 0, width, height) // 绘制canvas  
    const dataURL = canvas.toDataURL('image/jpeg') // 转换为base64  
    // 传递数据给逻辑层  
    ownerInstance.callMethod('getDataURL', {  
      dataURL: dataURL  
    })  
  })  
  video.addEventListener('error', err => {  
    console.log('视频加载失败', err)  
  })