canvas得到base64图片：

图片.png

    getVideo () {
      // 获取上传文件标签
      let filesId = document.getElementById('videoupload')
      // 获取音频标签
      let video = document.getElementById('video')
      this.fileDetail = filesId.files
      let url = this.getFileURL(filesId.files[0])
      if (url) {
        // 给video标签设置src
        video.src = url
      }
      var canvas = document.getElementById('myCanvas') // 获取 canvas 对象
      const ctx = canvas.getContext('2d') // 绘制2d
      video.crossOrigin = 'anonymous' // 解决跨域问题，也就是提示污染资源无法转换视频
      video.currentTime = 1 // 第一帧
      video.oncanplay = () => {
        canvas.width = video.clientWidth // 获取视频宽度
        canvas.height = video.clientHeight // 获取视频高度
        // 利用canvas对象方法绘图
        ctx.drawImage(video, 0, 0, video.clientWidth, video.clientHeight)
        console.log(canvas, 'canvas')
        // 转换成base64形式
        var oGrayImg = canvas.toDataURL('image/png') // 截取后的视频封面
        this.videoImg = [oGrayImg]
//base64转成png格式图片文件
        let name = this.fileDetail.name // 定义文件名字（例如：cober.png）
        function dataURLtoFile (dataurl, filename = 'file') {
          let arr = dataurl.split(',')
          let mime = arr[0].match(/:(.*?);/)[1]
          let suffix = mime.split('/')[1]
          let bstr = atob(arr[1])
          let n = bstr.length
          let u8arr = new Uint8Array(n)
          while (n--) {
            u8arr[n] = bstr.charCodeAt(n)
          }
          return new File([u8arr], `${filename}.${suffix}`, {
            type: mime
          })
        }
        var base64Img = oGrayImg // base64编码的图片
        console.log(oGrayImg, 'oGrayImg')
        var imgFile = dataURLtoFile(base64Img, name)
        console.log('imgFile====>', imgFile)
//发送到服务器
        var param = new FormData()
        param.append('file', imgFile)
        this.$axios
          .post('http://192.168.3.12:8026/video_cover.php', param)
          .then((res) => {
            console.log('success')
            console.log(res)
            var resData = res.data
            this.videoImg = [resData.data.url]
            this.videoImgObj = resData.data
            console.log(resData.data, 'obj', this.videoImgObj)
          })
          .catch((err) => {
            console.log('failed', err)
          })
      }
    },

    getFileURL (file) {
      let getUrl = null
      if (window.createObjectURL !== undefined) {
        getUrl = window.createObjectURL(file)
      } else if (window.URL !== undefined) {
        getUrl = window.URL.createObjectURL(file)
      } else if (window.webkitURL !== undefined) {
        getUrl = window.webkitURL.createObjectURL(file)
      }
      return getUrl
    },