media_preview_generator

_{Plex, Jellyfin and Emby web players on test servers, each paused mid-scrub on the same film. The thumbnails were made by this app. Tears of Steel, (CC) Blender Foundation | mango.blender.org, CC BY 3.0.}

What it does

Plex, Emby and Jellyfin can make preview thumbnails themselves, but they do it inside the server, mostly on the CPU, and mostly on a schedule. On a big library that can take days, and the episode that arrived tonight can sit with a blank timeline until the next maintenance window.

Media Preview Generator makes them on your GPU, for each file as it arrives. When more than one server holds the same file, it decodes it once and writes each server’s own format.

It also adds Skip Intro and Skip Credits. It finds each file’s intro and end credits once and sends the markers to every server that has the file. When it isn’t sure, it sends nothing; you can add or adjust a marker in the Inspector.

The GPU can be in another machine. Add it as a worker node; the app keeps the queue and every write.

What it looks like

It finds every server with that file

One GPU pass per file

Each server gets its own format

It waits for slow servers

_{App screenshots come from a test setup with made-up servers; the job titles are open films.}

Features

GPU first, CPU when needed

• Every GPU you pass in. NVIDIA, Intel and AMD on Linux; NVIDIA on Windows through WSL2.
• Named worker groups. Pick each group’s devices, job types, worker count and weekly hours. Worker guide.
• Remote nodes. Use a GPU or CPU on another machine as a worker node. For a Plex on another machine, including Plex on Windows, a Plex database node opens Plex’s database beside Plex. The app keeps the queue, tokens and every write. Nodes guide.
• CPU fallback built in. A file one GPU can’t decode tries your other GPUs first, then the CPU.
• Key-frame skipping. Jumps between key frames when a file’s key-frame spacing allows it.

Starts on its own

• Webhooks. Sonarr, Radarr, Sportarr, Tdarr, FileFlows, Plex (Plex Pass), Emby (Premiere) and Jellyfin, or any JSON with a path. Sonarr, Radarr and the three servers can share one URL.
• Schedules. Recently Added polling, plus cron and interval schedules.
• Process a file or folder. Search your servers by title (a whole show, a movie or one episode), or browse the media folders, and make previews for just those.
• Plex without waiting for a scan. File/folder jobs and path-based webhooks generate from the media itself, even while Plex is offline or has not indexed the file.
• Retries and skips. Retries after 1, 2, 5, 15 and 60 minutes by default while a server indexes a new file, and skips files whose previews are current.

Every server from one decode

• Each server’s own format. A BIF in Plex’s data folder, a BIF next to the video for Emby, and Jellyfin trickplay tiles (next to the video, or in Jellyfin’s data folder with the companion plugin).
• Setup Health. Checks each server’s settings and offers fixes one library at a time.

Choose what to generate. Filter manual or scheduled library scans by date added, keep the most recent X available TV seasons, or select a movie release-year range. Combine filters while keeping existing previews. See the library-scan guide.

Right colours

• HDR tone mapping. Tone-maps HDR10, HLG and HDR10+, and uses the HDR10 layer of Dolby Vision profiles 7 and 8. Profile 5 needs a GPU with a hardware Vulkan driver.

Skip Intro and Skip Credits

• Found once, sent to every server. Finds intros and end credits from the file’s chapters, online skip databases (TheIntroDB, IntroDB.app, SkipDB), the season’s theme song or the credit roll itself (read on the GPU when that’s faster), then sends the markers to every server. When it isn’t sure, it sends nothing instead of a guess; you can add or adjust a marker in the Inspector. Off until you turn it on for a server.
• Yours to correct. Tools → Inspector adjusts, adds and locks a file’s markers by hand, and Setup Health checks each server’s Intro & Credits setup.
• Plex. Needs Plex Pass on the server, and for viewers (or their Plex Home). The app runs on the Plex machine, or next to it through a Plex database node.
• Jellyfin. Jellyfin 10.11 or 12.0, with the Media Preview Bridge plugin (the one trickplay uses).
• Emby. Emby 4.9 or 4.10, with the Media Preview Bridge for Emby plugin. Skip Intro needs Emby Premiere; Skip Credits doesn’t.

Plex loudness

• Loudness analysis. Measures audio tracks on CPU worker groups and stores the results in Plex. Off until you turn it on for a Plex 1.43.4.x or 1.43.5.x server; independent of Intro & Credits.

Where it fits

Plex chapter thumbnails and loudness write Plex’s database, so they need this app on the Plex machine or a Plex database node beside it.

It sits next to Sonarr, Radarr and Tdarr and takes over the media server’s own preview job. Once it runs, the server’s own generation is the same work done twice. The app’s Setup Health tab says which setting to turn off on each server, and which to leave on: switching Jellyfin’s trickplay off deletes the tiles this app wrote. If your server’s own generator keeps up, you don’t need this: see how it compares.

Quick start

You’ll need: Docker · Plex, Emby or Jellyfin (Jellyfin 10.10 or newer), reachable from the container · write access where previews go: Plex’s data folder, or the media folder for Emby and Jellyfin. A GPU is optional: its driver on the host, plus the NVIDIA Container Toolkit for NVIDIA on Linux.

docker run -d \
  --name media-preview-generator \
  --restart unless-stopped \
  -p 8080:8080 \
  --device /dev/dri:/dev/dri \
  -e PUID=1000 -e PGID=1000 \
  -v /path/to/media:/media \
  -v /path/to/plex/config:/plex \
  -v /path/to/app/config:/config \
  stevezzau/media_preview_generator:latest

• Intel or AMD: --device /dev/dri as above. NVIDIA: --gpus all -e NVIDIA_VISIBLE_DEVICES=all -e NVIDIA_DRIVER_CAPABILITIES=all instead. No GPU, or on Windows or macOS? Delete the --device /dev/dri line.
• Plex writes into /plex, so the media can be :ro. Emby, and Jellyfin in its default layout, write next to each video, so for them the media mount must be read-write. No Plex? Drop the /plex mount.
• Open http://YOUR_IP:8080 and sign in with the token saved in auth.json in your app config folder (or pin your own with -e WEB_AUTH_TOKEN=...), then follow the setup wizard.
• The image is stevezzau/media_preview_generator. The double z is the Docker Hub account’s name, not a typo.

Docker Compose, Unraid and GPU details: Getting started.

Documentation

The docs are also a website: mediapreviewgenerator.dev.

Page	What’s in it
Getting started	Docker, GPUs, mounts, Unraid, networking
How it compares	Plex, Jellyfin and Emby built-in generation, side by side
Guides	The web UI, webhooks, schedules, troubleshooting
Remote nodes	Another machine’s GPU, and Plex on another machine or Windows
Multi-server	Plex, Emby and Jellyfin from one instance
Reference	Every setting, environment variable and API endpoint
FAQ	Windows, GPUs, RAM, skipped files
Why Plex previews are slow	What Plex does, and what to change
Plex previews with a GPU	Moving Plex’s preview job to a GPU
Faster Jellyfin trickplay	Jellyfin’s own settings first, then a GPU
Emby BIF previews with a GPU	Emby BIFs made on a GPU, next to each video
Previews on Sonarr or Radarr import	Webhooks, quiet period, retries
HDR and Dolby Vision previews	Tone mapping, and the Dolby Vision 5 caveat
Skip Intro and Skip Credits	What each server needs, how they’re found, limits

Support the project

It’s free and MIT licensed. Helping is optional.

• Star it on GitHub: free, and it’s how other server owners find it.
• Buy me a coffee on Ko-fi: no account needed.

Get help

• Previews don’t show up? Open the server’s Setup Health tab in the app. It names the setting that’s in the way.
• Not sure it’s a bug? Ask in Discussions.
• Found a bug? Open an issue with the app version and what you tried.

License

MIT, see LICENSE. Development is AI-assisted (Claude); every change is reviewed and tested.