Generating new chapter thumbnails for weeks

Plex Media Server NAS & Devices
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Server Version#: Latest (4.87.2)
Player Version#: Latest Android (9.9.0.35519)

For a couple of weeks my Plex running in Docker (plexinc/pms-docker) on a Synology is using up a lot of resources to generate chapter thumbnails.

The log files are completely full with “Generated new chapter thumbnails for xxx”, where xxx is a new movie/episode every few minutes or hours.

Since this is running for weeks I don’t expect it to end. Any idea what can be wrong?

I already tried to:

  • Move all movies/series, clear/clean Plex data. Then move the files back to trigger the process again.
  • Reset the Docker image

But nothing seems to work…

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Please verify the Plex Media Server version via Settings → Server_Name → General or Authorized Devices.
4.87.2 is the version for Plex Web.

Is it just chapter thumbnails or also video preview thumbnails?

Video preview thumbnail generation will take some time for each file. Plex creates a thumbnail for every two seconds of video.

Moving the movies/series will simply restart the process from the beginning for each file you moved.

If desired, you can configure Plex to generate thumbnails only during scheduled maintenance hours.

Go to Settings → Library.

Change Generate video preview thumbnails and Generate chapter thumbnails to As A Scheduled Task (or Never to completely disable the process).

Thumbnail generation will run during the hours configured in Settings → Scheduled Tasks.

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Here’s an example from my system.

PMS 1.29.2.6334, native, not in Docker.
Synology DS918+, DSM 7.1.1.42962

Avengers: Endgame (2019): 3 hours, 1 minute

Preview thumbnail generation begins: 12:47:49
Preview thumbnail generation ends: 13:35:07
Duration: 47:18

One of my movie libraries has ~2600 hours of video. At a preview generation rate of ~15.67 minutes per hour of video, it would take ~7 days to generate thumbnails for all the movies.

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Thanks!
My PMS version is 1.29.1.6316. It is running on a Synology 920+ which has hardware encoding enabled, and it takes about 30% of CPU while generating tumbnails. But that is slowing down the whole system.
I’m not sure whether it is about chapter or video preview thumbnails, how can I check that?

I have about 500 hours of video in total, so that is 5x less than you have, but it is running longer than a week. Generating thumbnails for most episodes take 5-15min, but some also take more than an hour. But quite a big part is 4K HDR, that might make a difference.

Either way you already helped me a lot by limiting the generation to the nights. That way it is not disturbing that much, and if there is no easy solution I can let it run for the coming period to see if it stops by itself.

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Chapter thumbnails should be quick, just a two or three minutes per movie.

The Activity icon in Plex Web will have a spinning circle when either is being generated. If you click on it you’ll see the activity listed. It will say something like “Generating chapter thumbnails for movie_name” or “Generating video preview thumbnails for movie_name.”

You can also see the activity Plex Media Server.log file:

Video preview thumbnails are easy to spot because there’s an entry for every 0.1% of progress. :rofl:
If you search for the activity string, you can find the start/stop times.

Video Preview Thumbnails

Oct 31, 2022 12:47:49.377 [0x7f1fd70dbb38] DEBUG - Activity: registered new activity e61fbb38-8de0-4e5b-bc50-abe35236ec8b - "Generating video preview thumbnails" (Memory Usage: 56.0 MB/1352.0 MB)
...
Oct 31, 2022 12:53:13.627 [0x7f1fd67f8b38] DEBUG - [Req#964/Transcode/bif/e61fbb38-8de0-4e5b-bc50-abe35236ec8b] Activity: updated activity e61fbb38-8de0-4e5b-bc50-abe35236ec8b - completed 10.3% - Generating video preview thumbnails (Memory Usage: 66.0 MB/1545.0 MB)
...
Oct 31, 2022 13:35:07.053 [0x7f1fd70dbb38] DEBUG - Activity: Ended activity e61fbb38-8de0-4e5b-bc50-abe35236ec8b (Memory Usage: 67.0 MB/1262.0 MB).

Chapter Thumbnails

Oct 31, 2022 12:47:49.361 [0x7f1fd72deb38] DEBUG - Activity: registered new activity 9629cff4-dbc7-45f0-ac45-df28da0768db - "Generating video chapter thumbnails" (Memory Usage: 56.0 MB/1350.0 MB)
...
Oct 31, 2022 12:50:35.692 [0x7f1fd72deb38] DEBUG - Activity: Ended activity 9629cff4-dbc7-45f0-ac45-df28da0768db (Memory Usage: 58.0 MB/1545.0 MB).
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I’ve now set the tasks (video preview and chapter thumbnails) to run between 0:00 and 9:00, but I don’t see that back in the logs.

I am however a bit surprised by the number of errors and warnings in the log (see attached). Many problems with transcoding/decoding, metadata, XML, etc

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