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 10.10.7 (Docker)
Ubuntu 24.04.2 LTS w/HWE
Intel i3 12100
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
4x WD Red Pro 6TB CMR in RAIDZ1