上传视频并截图，跨域报错的解决办法

跨域报错的缘由

最开始上传视频成功后，video标签的src会直接引入上传后的服务端资源地址，而后使用canvas截图就发生了跨域报错的提示。

Failed to execute 'toDataURL' on 'HTMLCanvasElement': Tainted canvases may not be exported.

按网上说的方法设置video标签的属性 crossorigin="anonymous",仍是报错，缘由是服务端的请求头没设置，不容许跨域访问。

Failed to load http://xxxx.oss-cn-shenzhen.aliyuncs.com/2018/08/22/1749/VU0SL0msslJvN1q3YNN2fmr1E4zmmE0vmHTV7A9s.mp4: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:8080' is therefore not allowed access.

解决办法： 视频上传成功后，不要引入线上地址，仍然使用本地视频地址，便可解决跨域问。

完整代码

<template>
  <div>
    <video ref='videoView' crossorigin="anonymous" v-show="videoId" :src="videoPath" controls="controls" class="video-upload-post-preview m-box-center m-box-center-a image-wrap more-image img3"></video>
    <input ref='videofile' id="selectvideo" type="file" name="file" @change="uploadVideo" class="upload__input m-rfile">
  </div>
</template>

<script>
  import sendImage from "@/util/SendImage.js";
  export default {
    data() {
      return {
        videoId: "",
        videoPath: "",
        videoCover: ""
      }
    },
    methods: {
      uploadVideo(e) {
        let file = e.target.files[0];
        sendImage(file)
          .then(id => {
            // console.log(id)
            this.videoId = id
            this.videoPath = URL.createObjectURL(file)
            setTimeout(() => {
              this.captureImage(file);
            }, 300);
          })
          .catch(e => {
            this.$Message.error("上传失败，请稍后再试");
          });
      },
      captureImage(file) {
        let video = this.$refs.videoView;
        // console.log(this.$refs, video)
        var canvas = document.createElement("canvas"); //建立一个canvas 
        canvas.width = video.videoWidth * 0.8; //设置canvas的宽度为视频的宽度 
        canvas.height = video.videoHeight * 0.8; //设置canvas的高度为视频的高度 
        canvas.getContext('2d').drawImage(video, 0, 0, canvas.width, canvas.height); //绘制图像 
        let imgBase64 = canvas.toDataURL()
        let imgFile = this.dataToFile(imgBase64)
        // console.log('img', imgFile)
        sendImage(imgFile)
          .then(id => {
            this.videoCover = id
          })
          .catch(e => {
            this.$Message.error("上传失败，请稍后再试");
          });
      },
      dataToFile(urlData) {
        var bytes = window.atob(urlData.split(',')[1]); //去掉url的头，并转换为byte  
        //处理异常,将ascii码小于0的转换为大于0  
        var ab = new ArrayBuffer(bytes.length);
        var ia = new Uint8Array(ab);
        for (var i = 0; i < bytes.length; i++) {
          ia[i] = bytes.charCodeAt(i);
        }
        return new Blob([ab], {
          type: 'image/jpg'
        });
      }
    }
  }
</script>