How to set default load width and height before loading

Hi,
Is that possible to change the default size of height and width when a video not loading?

1.Sometimes the video is preparing,the size shows too small
https://pasteboard.co/9KKotBA4F.jpg

2.It should be like this ,when a video does not ready,the default screen size seems as it finish loading,for example,a video is 1024*768,whatever the video loaded or not,the screen may always is 1024*768.
https://pasteboard.co/9KLfin4HG.jpg

Thanks in advance.

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