vue 截取视频第一帧 当做视频封面

组件代码：

<el-form-item ref="videocontentvideo" style="display:none;">
  <img :src="imgurl">
  <video width="320" height="240" controls id="upvideo">
  </video>
  <img :src="modlevidel" />
</el-form-item>

<el-form-item class="upload-demo-content" v-show="formLabelAlign.type==2">
    <el-upload class="upload-demo" :limit="1" :on-exceed="exceedhandle" drag :file-list="filsListArray" :action="configuploadurl"
     :on-success="successuploadhandle" accept="video" name="fileList" :before-upload="beforeUploadVideo">
        <i class="el-icon-upload"></i>
        <div class="el-upload__text">将视频文件拖到此处，或
            <em>点击上传</em>
        </div>
        <div class="el-upload__tip" slot="tip"></div>
    </el-upload>
</el-form-item>

successuploadhandle(response, file, fileList) {
  this.formLabelAlign.video = this.modlevidel =
    response.data.fileList[0].url;
  this.filsListArray = [];
  this.filsListArray.push({
    name: this.formLabelAlign.video,
    url: this.formLabelAlign.video
  });
  this.findvideocover();
},
exceedhandle(files, fileList) {
    this.$message.error("只能上传一个视频额");
},

 beforeUploadVideo(file) {
      if (
        [
          "video/mp4",
          "video/ogg",
          "video/flv",
          "video/avi",
          "video/wmv",
          "video/rmvb"
        ].indexOf(file.type) == -1
      ) {
        this.$message.error("请上传正确的视频格式");
        return false;
      }
    },

主要代码：

   findvideocover() {
      let _this = this;
      this.$nextTick(() => {
        let video = document.getElementById("upvideo");
        let source = document.createElement("source");
        // source.src = require("../../assets/5b086751dbb7af1ea8fa8d05e66fe5c3.mp4");this.formLabelAlign.video
        source.src = this.formLabelAlign.video;
        source.type = "video/mp4";
        video.appendChild(source);
        video.addEventListener("loadeddata", function() {
          var canvas = document.createElement("canvas");
          canvas.width = "320";
          canvas.height = "320";
          canvas
            .getContext("2d")
            .drawImage(video, 0, 0, canvas.width, canvas.width);
          var img = document.createElement("img");
          let imgsrc = canvas.toDataURL("image/png");
          _this.Videoframehandle(imgsrc.split(",")[1]);
        });
      });
    },

视频预览

 showvideohandle() {
      this.$alert(
        `<video width="320" height="240" controls>
                      <source src="${
                        this.filsListArray[0].url
                      }"  type="video/mp4">
                      您的浏览器不支持 HTML5 video 标签。
                    </video>`,
        "视频预览",
        {
          dangerouslyUseHTMLString: true
        }
      );
    },