Why does html5 video display blank space on the mobile and the first image on pc?

In the example of

W3C, the first image is displayed on pc. If you open it with your mobile phone, it will be blank, and you won"t get the image until you click play. What"s the reason?

Mar.30,2021

browser implementation is different from webview implementation
if you want a uniform performance, you may need to define poster, or even implement poster yourself

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