docs/superpowers/plans/2026-07-26-jellyfin-hw-transcoding.md

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+# Jellyfin Hardware Transcoding (jupiter) Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Give jupiter's Jellyfin service access to the Intel iGPU's VAAPI render node so Quick Sync hardware transcoding can be enabled, instead of every transcode falling back to CPU.
+
+**Architecture:** One NixOS module change (`modules/environments/jellyfin/default.nix`) grants the `jellyfin` systemd service supplementary access to the `video`/`render` groups and installs `libva-utils` for verification. This is declarative and build-verifiable from the Mac. Enabling Quick Sync inside Jellyfin's own dashboard, and the on-machine verification, is a manual step run by the user on jupiter after deploy — the NixOS module has no option for it and this environment's convention is that the assistant never SSHes into jupiter directly (see `docs/superpowers/specs/2026-07-26-jellyfin-hw-transcoding.md`).
+
+**Tech Stack:** NixOS (flake-parts), nixpkgs `services.jellyfin` module, VAAPI/`intel-media-driver`, `libva-utils`.
+
+## Global Constraints
+
+- No SSH from the assistant into jupiter — all on-machine commands are given to the user to run and paste back.
+- Follow the existing profile pattern in `modules/environments/jellyfin/default.nix` (`config = lib.mkIf cfg.enable { ... }`); don't introduce a new toggle option — hardcode the hardware-acceleration wiring on, per the approved spec.
+- Verify locally via `nix eval` / `nix build` before asking the user to deploy.
+
+---
+
+### Task 1: Grant Jellyfin access to the iGPU and verify the build
+
+**Files:**
+- Modify: `modules/environments/jellyfin/default.nix`
+
+**Interfaces:**
+- Produces: `systemd.services.jellyfin.serviceConfig.SupplementaryGroups = [ "video" "render" ];` — verified via `nix eval` in Step 2.
+
+- [ ] **Step 1: Add the device-access config and `libva-utils` package**
+
+Read the current file first (`modules/environments/jellyfin/default.nix`), then edit the `config = lib.mkIf cfg.enable { ... }` block so it reads:
+
+```nix
+  config = lib.mkIf cfg.enable {
+    services.jellyfin = {
+      enable = true;
+      openFirewall = true;
+    };
+
+    environment.systemPackages = [ pkgs.libva-utils ];
+
+    my.homepage.services = [
+      {
+        group = "Media";
+        name = "Jellyfin";
+        description = "Media server";
+        href = "http://${hostName}:${toString port}";
+        icon = "jellyfin.png";
+      }
+    ];
+
+    systemd.services.jellyfin = {
+      after = [ "network-online.target" ];
+      serviceConfig.SupplementaryGroups = [
+        "video"
+        "render"
+      ];
+    };
+  };
+```
+
+Note the two existing `systemd.services.jellyfin` keys (`after`) and the new `serviceConfig.SupplementaryGroups` now live in the same attrset — don't create a second `systemd.services.jellyfin = { ... }` block, it would overwrite the first.
+
+- [ ] **Step 2: Verify the rendered config with `nix eval`**
+
+Run (from the repo root on the Mac):
+
+```bash
+nix eval '.#nixosConfigurations.jupiter.config.systemd.services.jellyfin.serviceConfig.SupplementaryGroups' \
+  --extra-experimental-features 'nix-command flakes'
+```
+
+Expected output: `[ "video" "render" ]`
+
+- [ ] **Step 3: Verify the machine still builds**
+
+Run:
+
+```bash
+nix build '.#nixosConfigurations.jupiter.config.system.build.toplevel' \
+  --extra-experimental-features 'nix-command flakes' --no-link
+```
+
+Expected: build succeeds with no errors (may take a while; watch for any evaluation error mentioning `jellyfin` or `libva-utils`).
+
+- [ ] **Step 4: Format and commit**
+
+```bash
+nixfmt-rfc-style modules/environments/jellyfin/default.nix
+git add modules/environments/jellyfin/default.nix
+git commit -m "feat(jellyfin): grant iGPU access for Quick Sync hardware transcoding"
+```
+
+---
+
+### Task 2: Deploy on jupiter and enable Quick Sync (user-executed)
+
+**Files:** none (on-machine deploy + Jellyfin dashboard UI)
+
+**Interfaces:**
+- Consumes: the `SupplementaryGroups` change from Task 1, already merged into the flake.
+
+These steps run **on jupiter**, by the user — paste the output back so we can confirm each one before moving to the next.
+
+- [ ] **Step 1: Deploy**
+
+```bash
+sudo nixos-rebuild switch --flake '.#jupiter'
+```
+
+Expected: switch succeeds, no errors mentioning `jellyfin`.
+
+- [ ] **Step 2: Confirm the service picked up the new groups**
+
+```bash
+systemctl show jellyfin -p SupplementaryGroups
+systemctl status jellyfin --no-pager
+```
+
+Expected: `SupplementaryGroups=video render` (order may vary) and the service is `active (running)`.
+
+- [ ] **Step 3: Confirm VAAPI driver loads**
+
+```bash
+vainfo
+```
+
+Expected: output starts with something like `vainfo: VA-API version: 1.x` and `Driver version: Intel iHD driver`, followed by a list of supported VAProfiles/VAEntrypoints (e.g. `VAProfileH264Main : VAEntrypointVLD`, `VAEntrypointEncSlice`).
+
+If this instead prints a permissions or "no VA display" error, paste it back — that means the group grant isn't reaching the process and Task 1 needs a follow-up fix (e.g. the jellyfin service may be more sandboxed than expected, requiring an explicit `DeviceAllow=char-drm rw` in `serviceConfig` as well).
+
+- [ ] **Step 4: Enable Quick Sync in the Jellyfin dashboard**
+
+In the Jellyfin web UI:
+1. **Dashboard → Playback**.
+2. Hardware acceleration: **Intel QuickSync (QSV)**.
+3. VA-API device: `/dev/dri/renderD128`.
+4. Enable hardware decoding for the codecs your library uses (H264 at minimum).
+5. If the library has HDR content, enable tone-mapping.
+6. Save.
+
+- [ ] **Step 5: Functional check**
+
+Play a file that requires transcoding (or force a lower quality in the client's playback settings to trigger one), then:
+
+```bash
+journalctl -u jellyfin -n 50 --no-pager
+```
+
+Look for a line referencing `qsv` or `vaapi` in the transcode command. Separately, watch CPU usage (`htop`) during playback — it should stay low on the core doing the transcode, rather than pegging at 100%, since the iGPU is now doing the encode/decode work.
+
+## Self-Review Notes
+
+- Spec coverage: NixOS change (Task 1) ✓, manual dashboard step (Task 2 Step 4) ✓, verification via `vainfo`/build (Task 1 Step 2-3, Task 2 Step 3) ✓, functional check (Task 2 Step 5) ✓. Toggle option explicitly excluded per approved spec — not present, correctly.
+- No placeholders — every step has literal commands/code.
+- `SupplementaryGroups` key/value matches exactly between Task 1 (produced) and Task 2 (consumed/checked).