I am on mobile, but run the help file and go to the video section, you will find info there in what format you must use.
There is also an answer here on the forum of this exact problem.
When i get on my workstation i will help you in detail ;)
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Video Files (Movies)
The file formats that are playable depend on the operating environment, so please prepare the below 2 file formats with the same file name.
- WebM(.webm)
- MP4 (.mp4 encoded with H.264 codec)
* When creating a game that will be played on Windows or Mac, please prepare only the WebM file format. When creating a game that will be released on the web or made for Android/iOS, both file formats are required.