HTML5 video 上传预览图片视频如何设置、预览视频某秒的海报帧

/*预览*/
              $('.qtuploader__items').on('click', '[name="viewVideoPicBtn"]', function() {
    var parent = $(this).closest('.qtab__page');
    var video = $(this).closest('.qtuploader__itemsbd').find('video');
    var srcStr = '', htmlStr = '';
    if($(this).siblings('.qtuploader__picinputbox').hasClass('is-error')){
      $.fn.toast({
        'parentDom': parent,
        'classes': 'isorange',
        'top': '0',
        'spacing': 0,
        'toastContent': '请设置正确范围的海报帧',
        'autoHide': 3000,
        'position': {
          'top': '5px',
          'left': '50%'
        }
      });
      return;
    }
    if (video.length > 0) {
      var thumbHeight = setSize(video)[0];
      var thumbWidth = setSize(video)[1];
      srcStr = video.attr('src');
      htmlStr = '<div class="qtuploader__view"><div class="qtuploader__mask"></div><div class="qtuploader__thumb" style="width:' + thumbWidth + 'px;height:' + thumbHeight + 'px;margin:0 auto;"><video controls width="' + thumbWidth + '" height="' + thumbHeight + '" src="' + srcStr + '">您的浏览器不支持 video 标签</video></div></div>';
    }
    parent.append(htmlStr);
    parent.find('.qtuploader__view video')[0].currentTime = $(this).siblings('.qtuploader__picinputbox').find('.qtuploader__picinput').val();
    parent.find('.qtuploader__view').fadeIn();
  });
  /*设置海报帧预览时间*/
  $('.qtuploader__items').on('keyup', '.qtuploader__picinput', function() {
    var parent = $(this).closest('.qtuploader__picinputbox');
    var video = $(this).closest('.qtuploader__itemsbd').find('video');
    var strVal = $.trim($(this).val());
    console.log(strVal)
    if (strVal == '') {
      parent.addClass('is-error');
      parent.find('.qverify__font').text('请设置海报帧');
    } else if (!(/^[0-9]*$/.test(strVal))) {
      parent.addClass('is-error');
      parent.find('.qverify__font').text('请输入数字');
    } else if (video.length > 0 && strVal > video[0].duration) {
      parent.addClass('is-error');
      parent.find('.qverify__font').text('不超过(' + video[0].duration + ')');
      console.log('111---' + video[0].duration)
    } else {
      parent.removeClass('is-error');
      parent.find('.qverify__font').text('请设置海报帧');
    }
  })
  /*关闭预览*/
  $(document).undelegate('.qtuploader__mask', 'click');
  $(document).delegate('.qtuploader__mask', 'click', function() {
    $(this).closest('.qtuploader__view').fadeOut('normal', function() {
      $(this).closest('.qtuploader__view').remove();
    })
  })
  /*设置预览大小*/
  function setSize(element) {
    var thumbWidth = 0, thumbHeight = 0, arr = [];
    var winWidth = $(window).width(), winHeight = $(window).height();
    var imgWidth = element.width(), imgHeight = element.height();
    if (imgWidth > imgHeight) {
      thumbHeight = parseInt(winHeight - 200);
      thumbWidth = parseInt((1920 * thumbHeight) / 1080);
    } else {
      thumbHeight = parseInt(winHeight - 200);
      thumbWidth = parseInt((1080 * thumbHeight) / 1920);
    }
    arr.push(thumbHeight, thumbWidth)
    return arr;
  }