Step 1: Obtain the ffmpeg-jellyfin Binary

Locate the Jellyfin Binary: Find the actual ffmpeg executable used by your working Jellyfin container. It is typically located in a directory like /usr/lib/jellyfin-ffmpeg/ inside the container, or it may be available as a portable download.
Place on Unraid Share: Extract the downloaded archive and place the single ffmpeg executable file into a designated location on your Unraid server, such as a dedicated folder on your cache drive (e.g., /mnt/user/appdata/custom_binaries/ffmpeg-jf/).

Step 2: Map the Binary into the Tdarr Node Container

You need to tell the Tdarr Node container where to find this external ffmpeg file by adding a Volume Mapping in the Docker settings for your Tdarr Node (or Tdarr Server, if running as a single container).
Edit Tdarr Node Docker: In the Unraid WebUI, go to Docker, click on the Tdarr Node container, and select Edit.
Add Path Mapping: Add a new Path (Volume Mapping) under "Add another Path, Port, Variable, Label or Device":
Container Path: /binaries/ (This is the virtual path inside the Docker container where Tdarr will look for the binary).
Host Path: /mnt/user/appdata/custom_binaries/ffmpeg-jf/ (Replace this with the actual location you created in Step 1).
Apply/Save: Click Apply to restart the Tdarr Node container with the new mapping.

Step 3: Configure Tdarr to Use the Custom Path

Finally, you tell Tdarr's settings to use the file at the mapped container path instead of its internal, problematic binary.
Open Tdarr WebUI: Navigate to the Tdarr web interface.
Go to Node Settings: Go to the Nodes tab, select your Tdarr Node, and click Edit.
Set Custom FFmpeg Path: Under the Node settings, look for the field named FFmpeg Path (or equivalent, depending on your Tdarr version).
Enter the Container Path: Set the value of the FFmpeg Path to the full path of the binary inside the container: /binaries/ffmpeg
Save Changes and restart the Tdarr Node.