I noticed my home servers SSD running out of space and it ended up being my Jellyfin Docker container which wasn’t clearing the directory for transcodes in /var/lib/jellyfin/transcodes correctly.
I simply created a new directory on my media hard drive and bind mounted the above mentioned directory to it. Now Jellyfin got over 1 TB of free space to theoretically clutter. To prevent this I simply created a cronjob to delete old files in case Jellyfin isn’t.
/usr/bin/find /path/to/transcodes -mtime +1 -delete
Easy!
tmpfs is the filesystem you are looking for. You can mount it like any other filesystem in /etc/fstab.
tmpfs /path/to/transcode/dir tmpfs defaults 0 0