Please make a specific app connector for video content stored on Microsoft Stream / SharePoint. Or improve the iFrame embed app to support Stream content better.
It is currently possible to embed videos using a Microsoft Stream iFrame, but there is no thumbnail, and the frame is neither re-sizeable and doesn’t match the aspect ratio of the video file.
At an absolute minimum please change the default aspect ration for an iFrame to 16:9 rather than the current 20:9 or whatever it is.