# What are video pre-roll ads?

<div data-elink-language-switch="1" id="bkmrk-%E4%B8%AD%E6%96%87" style="border:1px solid #d6d9de;border-radius:6px;padding:10px 12px;margin:0 0 18px 0;background:#f8fafc;font-size:14px;">[中文](/books/250cf/page/9bf31)</div><span style="font-size:15px;">Video posters refer to the preview images (i.e., video cover images) displayed before video playback. You can set them in \[Content\] - \[Videos\] - \[Create New Video\] - \[Video Poster\]. To ensure display quality, the uploaded files must be JPG or PNG files smaller than 5MB, and the file size should be set to 750\*422px or in a 16:9 aspect ratio.</span>

![image (7).png](https://wechatapppro-1252524126.file.myqcloud.com/help_document/image/ueditor/63491200_1640269572.png ".png")

<span style="font-size:15px;">Meanwhile, it is recommended that you do not select transparent images as preview images, as this may cause abnormal display on your section pages. If you do not upload a video poster, the first frame of the video will be used by default.</span>