如果你需要需要在 SharePoint Online 中，上传一个 视频资源，并在自己的定制页面中，引用这个视频，你可以通过如下方法进行操作。
1. Open the SharePoint site and click on “Site Content” on the left panel.
2. Click the “New” button at the top of the site content page and click “Applications” on the menu.
3. Type “Repository” in the search box and click the Asset Library application in the search results.
4. Enter the name of the new asset library and click the “Create” button.
5. Click on the new asset library you created and upload the video file.
6. After uploading your video file, wait a moment and then refresh your page, now you will see a folder named by your video file.
7. Right-click on the video folder and click Details, and the details pane will appear on the right side of the screen.
8. Click “Edit All” in the details pane.
9. On the new page, click the “Change Thumbnails” link and select the “Capture Thumbnails from Video” option, and the new “Capture Thumbnails” button will appear at the top of the video player.
10. Play the video, when you are satisfied with the currently playing video as a thumbnail, click the “Capture Thumbnail” button, then click the “Save” button.
11. Enter the video folder, right-click on the video file, and click Copy Link.
12. Open a new blank page on your web browser and access the URL you just copied.
13. After the page loads the video content, re-copy the URL of the current webpage, temporarily save the URL, and later embed it as the URL of the video into the HTML page.
14. Go back to the SharePoint page, go to the Preview Image folder, right-click on the thumbnail image file, and click Copy Link.
15. Repeat the above steps to open a new blank page on your web browser and access your URL.
16. After the page loads the image content, re-copy the URL of the current webpage, temporarily save the URL, and later embed it as the URL of the video thumbnail into the HTML page.