Set own thumbnail for movie preview?

Is it possible to set my own thumbnails? I have hundreds of videos and the default preview generator does create thumbnails, but they can at times not be a helpful indicator of what the video contains. Is there any way, I can specify that it uses an image as the thumbnail?

Nextcloud version (eg, 20.0.5): 26
Operating system and version (eg, Ubuntu 20.04): 18.04
Apache or nginx version (eg, Apache 2.4.25): 2
PHP version (eg, 7.4): 8.1

Preview is enabled by adding the following to config.php:

‘enable_previews’ => true,

‘enabledPreviewProviders’ =>

array (