Projet page: https://github.com/jellyfin/jellyfin-ffmpeg
Patches: https://github.com/jellyfin/jellyfin-ffmpeg/tree/jellyfin/debian/patches

Extract jellyfin-ffmpeg git repository
$ git clone https://github.com/jellyfin/jellyfin-ffmpeg.git

$ git branch -a
* jellyfin
  remotes/origin/HEAD -> origin/jellyfin
  remotes/origin/jellyfin
  remotes/origin/jellyfin-4.4
  remotes/origin/jellyfin-5.1
$ git checkout jellyfin-4.4
Updating files: 100% (4584/4584), done.
Branch 'jellyfin-4.4' set up to track remote branch 'jellyfin-4.4' from 'origin'.
Switched to a new branch 'jellyfin-4.4'

Check that current ffmpeg matches jellyfin version
$ cat jellyfin-ffmpeg/VERSION 
4.4.2

Modify patches to be in -p0 mode:
cd debian/patches
$ sed -i -e 's?+++ jellyfin-ffmpeg/?+++ ?1' \
         -e 's?--- jellyfin-ffmpeg.orig/?--- ?1' \
         *.patch

Rename the patches:
$ i=1001 && ls -1 *.patch | while read LINE; do echo $(printf "%04d" $i)-jellyfin-$LINE; mv $LINE $(printf "%04d" $i)-jellyfin-$LINE; let i++; done

Test the patches on a clean ffmpeg 4.4 tree:
$ tar -jxvf ffmpeg-4.4.3.tar.bz2 
$ cd ffmpeg-4.4.3/
$ ls -1d ~/jellyfin-ffmpeg/debian/patches/*.patch | while read LINE; do patch -p0 < $LINE; done
