feat(video): 优化视频详情页加载逻辑

- 添加 v-if 条件渲染确保视频封面存在时才加载视频组件
- 设置 preload="metadata" 提高页面初始加载性能
- 保留原有事件监听器和样式配置

packageB/train/video/videoDetail.vue

@@ -9,7 +9,9 @@
 			<view class="video-detail-container">
 			    <!-- 视频播放组件 -->
 			    <view class="video-wrapper">
-					<video id="myVideo" :src="videoInfo.currentUrl" :poster="trainVideoImgUrl+ videoInfo.cover" @seeked="onSeeked"
+					<video v-if="videoInfo && videoInfo.cover" id="myVideo" :src="videoInfo.currentUrl" :poster="trainVideoImgUrl+ videoInfo.cover" @seeked="onSeeked"
+					
+                preload="metadata"
 						 enable-danmu controls style="width: 100%;" @pause="onPause" @timeupdate="onTimeupdate" @ended="onEnded"></video>
 			    </view>
 			</view>