You'd open the bash prompt for the Jellyfin container again. ffprobe is in the same folder as ffmpeg. Just run that command and provide a file path for the new video.
Jellyfin 10.10.6 (Docker)
Ubuntu 24.04 LTS
Intel i3 12100
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
3x WD Red Pro 6TB CMR in RAIDZ1 (JF Library)