marthsincemelee
84cec9e935
Jupiter's Intel iGPU is configured at the OS level but Jellyfin has no access to it, so transcodes run on CPU only and stutter. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
109 lines
3.8 KiB
Markdown
109 lines
3.8 KiB
Markdown
# Intel Quick Sync hardware transcoding for Jellyfin on jupiter
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## Problem
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Jellyfin streams stutter on jupiter whenever a client needs a transcode
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(unsupported codec/container, bitrate cap, or a client that can't
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direct-play). Transcoding currently runs entirely on CPU.
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jupiter's Intel iGPU is already usable at the OS level:
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- `hardware.graphics.enable = true` with `intel-media-driver` (the `iHD`
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VAAPI driver) is configured in
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`machines/jupiter/hardware-configuration.nix:20-27`.
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- The commented-out `i915.force_probe = "9a49"` kernel param there
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corresponds to a Quick-Sync-capable Intel UHD iGPU, confirming the
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hardware supports it.
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But `modules/environments/jellyfin/default.nix` never grants the
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`jellyfin` systemd service access to `/dev/dri`, so Jellyfin has no path
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to the GPU and silently falls back to software transcoding.
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## Goal
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Give the Jellyfin service access to the iGPU's VAAPI render node, so
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Quick Sync can be enabled in Jellyfin's own dashboard and transcodes are
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offloaded from the CPU.
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## Non-goals
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- Remote/external access or reverse-proxy tuning.
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- General CPU/RAM headroom review of jupiter.
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- A toggle option (`my.profiles.jellyfin.hardwareAcceleration.enable`) —
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jupiter only has the one iGPU, so this is hardcoded on rather than
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made configurable.
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## Design
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### NixOS change (declarative)
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In `modules/environments/jellyfin/default.nix`, inside the existing
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`config = lib.mkIf cfg.enable { ... }` block, grant the systemd service
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supplementary access to the `video` and `render` groups (the groups that
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own `/dev/dri/card*` and `/dev/dri/renderD*`):
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```nix
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systemd.services.jellyfin.serviceConfig.SupplementaryGroups = [
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"video"
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"render"
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];
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```
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This is additive to the existing `systemd.services.jellyfin.after = [
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"network-online.target" ];` block already in the file — both apply to
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the same service.
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Also add `libva-utils` to `environment.systemPackages` (or scoped to
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this module) so `vainfo` is available on jupiter to verify the driver
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loads correctly.
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### Manual step (not declarative)
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Jellyfin stores its transcoding/hardware-acceleration choice in its own
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internal `encoding.xml`, which the NixOS module does not expose as an
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option. After deploying the Nix change, one-time manual configuration in
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the Jellyfin dashboard is required:
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1. **Dashboard → Playback**.
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2. Hardware acceleration: **Intel QuickSync (QSV)**.
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3. VA-API device: `/dev/dri/renderD128`.
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4. Enable hardware decoding for the codecs your library actually uses
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(H264 at minimum; HEVC/VP9 depending on iGPU generation).
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5. If any HDR content exists in the library, enable tone-mapping — this
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is one of the more CPU-expensive operations Quick Sync can offload.
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## Verification
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Build-time (from the Mac, no SSH needed):
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```
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nix eval '.#nixosConfigurations.jupiter.config.systemd.services.jellyfin.serviceConfig.SupplementaryGroups' \
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--extra-experimental-features 'nix-command flakes'
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```
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Expect `[ "video" "render" ]`.
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On jupiter after `sudo nixos-rebuild switch --flake '.#jupiter'`:
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```
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systemctl status jellyfin
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journalctl -u jellyfin -n 50 --no-pager
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vainfo
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```
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`vainfo` should list the `iHD` driver and print supported VAEntrypoints
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(VLD decode / encode profiles for H264/HEVC).
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Functional check: play a file on a client that forces transcoding (or
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force it manually via Jellyfin's playback quality setting), then in
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Jellyfin's dashboard **Activity/Now Playing** panel confirm the
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transcode reason and check that CPU usage on jupiter (`htop`) stays low
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during playback rather than pegging a core — Quick Sync offload should
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show up as low CPU, some GPU (`intel_gpu_top`) activity instead.
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## Open items
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- Exact supported codec list depends on the iGPU generation (device ID
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`9a49`) — confirm via `vainfo` output once run, and enable only the
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hardware decode paths it actually reports.
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