H5中video获取第一帧如何作为封面

let result$('#uploadBtn').on('change', function (e) {

    const file = e.target.files    // console.log(file)

    let fr = new FileReader()

    fr.readAsDataURL(file[0]) //将文件读取为tata Url

    fr.onload = function (e) {

        result = e.target.result        // 视屏上传

        if (/video/g.test(file[0].type)) {

            $('.upload-img').show()

            $('.upload-img video').attr('src', result)

            $('.upload-file').hide()

         }

     }})function vSetImg(obj) {

     $(obj).removeAttr("poster");

     var vimg = $("<img/>")[0];

     captureImage(obj, vimg);

     $(obj).attr("poster", $(vimg).attr("src"));

     //展示获取的第一帧图片

     $(".upload-img img").attr("src", $(vimg).attr("src"));

     $('.upload-img video').hide()

     $('.upload-img img').show()}function captureImage(video, output) {

     const scale = 0.8

     try {

         var videocanvas = $("<canvas/>")[0];

         videocanvas.width = video.videoWidth * scale;

         videocanvas.height = video.videoHeight * scale;

         videocanvas.getContext('2d').drawImage(video, 0, 0, videocanvas.width, videocanvas.height);

         output.src = videocanvas.toDataURL("image/png");

         delete videocanvas;

     } catch (e) {

         output.src = "加载动画.gif";

     }}