Movie format for presentation

Putting together a presentation, but it will not import an mp4.
what video format is required?

The online Help can’t seem to find video in Impress. The built-in Help (might be an older version of Help) on my LibreOffice gives the following:

…you can choose Tools - Media Player to open the Media Player. Use the Media Player to preview all supported media files. Click the Apply button in the Media Player window to insert the current media file into your document.

Hope this helps. Cheers, Al