No preview for videos shorter than 4 seconds

No preview (thumbnail) is generated for videos shorter than 4 seconds. For longer videos it works perfectly. Can somebody reproduce?

Nextcloud version (eg, 12.0.2): 17.0.3
Operating system and version (eg, Ubuntu 17.04): Ubuntu 18.04.4 LTS
Apache or nginx version (eg, Apache 2.4.25): Apache 2.4.41
PHP version (eg, 7.1): 7.3 FPM
Additional info: ffmpeg present, previewgenerator active and working