docs(transcodes): document NVIDIA_VISIBLE_DEVICES + bind-propagation=shared conflict

--runtime=nvidia + NVIDIA_VISIBLE_DEVICES + bind-propagation=shared causes
"open /proc/self/mountinfo" init failure. Fix: --gpus device=UUID flag instead.

Transcodes/Manual-Transcoding.md

@@ -482,6 +482,41 @@ leave the container in a broken state where Emby refuses to start at all.
 # Re-adding the mount after a clean start works reliably.
 ```
 
+### Emby With NVIDIA GPU — bind-propagation=shared Fails to Start
+
+`--runtime=nvidia` combined with a `NVIDIA_VISIBLE_DEVICES` environment variable conflicts
+with `bind-propagation=shared`. Docker fails during container init with:
+
+```
+OCI runtime create failed: runc create failed: unable to start container process:
+error during container init: error jailing process inside rootfs:
+open /proc/self/mountinfo: no such file or directory
+```
+
+`--runtime=nvidia` alone (no `NVIDIA_VISIBLE_DEVICES` env var) does NOT cause this.
+The conflict requires both.
+
+**Root cause:** `NVIDIA_VISIBLE_DEVICES` triggers the NVIDIA container runtime to bind
+mount CUDA libraries and device nodes into the container namespace. This GPU device setup
+interferes with the mount namespace initialization that `bind-propagation=shared` requires.
+
+**Fix — replace the NVIDIA env var approach with the `--gpus` flag:**
+
+In the unRAID Docker template for Emby:
+
+1. **Extra Parameters** — remove `--runtime=nvidia`, add `--gpus` with the GPU UUID:
+   ```
+   --gpus device=GPU-62e1659d-1ed4-935f-3df3-4bb4339438f1 --pids-limit=0 \
+   --mount type=bind,source=/mnt/ram-transcode,target=/ext-ram-transcode,bind-propagation=shared
+   ```
+
+2. **Variables** — remove the `NVIDIA_VISIBLE_DEVICES` variable entirely.
+   The `--gpus` flag handles GPU assignment without the env var.
+
+`--gpus device=UUID` uses Docker's native GPU device flag (default runtime) rather than
+the full NVIDIA container runtime setup. The container still gets GPU access; it just
+skips the device mount phase that conflicts with `bind-propagation=shared`.
+
 ### Increasing Ramdisk Size After Initial Setup
 
 ```bash