Hi,
If it helps,
In my case, I get the definition of the schema that should contain the asset with the validation rules. On my front end I check the number of file, size, format, extension etc and warn the user before loading the media on squidex.
I have added validation rules to also check the video size when assigning assets to contents. This does not prevent someone from uploading an incorrect video, but it prevents assigning the video to the content.