Plex can't generate video & chapter thumbnails for one specific movie

[thirdgen89gta]

Server Version#: 1.30.0.6486
Player Version#: 1.59.1.3398-dab42972(Plex for Mac)
OS: Linux plexy 5.15.0-53-generic #59-Ubuntu SMP Mon Oct 17 18:53:30 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

Plex Media Server Logs_2022-12-21_08-57-50.zip (354.7 KB)

I’m trying to find out why with one specific movie, it seems Plex is unable to generate video & chapter thumbnails. It has no issues actually playing the movie itself, but the thumbnails are all black.

I’ve verified it doesn’t do this with another movie by duplicating some existing movies I recently added, but faking them out to match as a different movie, and it had no issues generating the video & chapter thumbnails with those. It’s just this one specific movie.

I’ve included the XML for the item, and logs from the most recent ingest after I did the Plex-dance to force a regeneration of thumbnails. Had to rename it to TXT, just drop the extension, its pure XML.

771430_ProjectAko3.xml.txt (14.7 KB)

[OttoKerner]

Interestingly, Plex seems to be covinced that it actually has valid thumbnail pictures. Otherwise there would be no thumb property in here:

<Chapter id="1" filter="thumb=1" index="1" startTimeOffset="0" endTimeOffset="137679" thumb="/library/media/1349392/chapterImages/1" />
<Chapter id="1" filter="thumb=1" index="2" startTimeOffset="137679" endTimeOffset="352769" thumb="/library/media/1349392/chapterImages/2" />
<Chapter id="1" filter="thumb=1" index="3" startTimeOffset="352769" endTimeOffset="707665" thumb="/library/media/1349392/chapterImages/3" />

Have you tried to remux the file using a current version of MKVtoolnix?
Followed by a complete Plex Dance to flush the invalid thumbnails out?

[thirdgen89gta]

Not exactly familiar with remuxing. I do have MKVtoolnix installed, I mostly use it for adding/adjusting chapter’s and steam names for things like commentaries and the like. Can you expand on remuxing a bit?

As for the thumbnails, I’ve been trying to locate the actual JPGs for the generated files to see if they exist. Is there a way to locate the exact Media folder based on item ID, or info in the XML?

I know they are in the /var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Media/localhost

I thought it might be in folder “1”, and looked at the most recently created bundle’s, but none of them are Project A-Ko.

I know the Item# is 771430.

And I thought the bundle name might be “5d77699d47dd6e001f6c7de3”, but can’t locate a bundle folder with that name in the “Media” folder.

[OttoKerner]

@thirdgen89gta

Can you expand on remuxing a bit?

Basically, just sending the file into MKVtoolnix and let it do its thing. Without changing or adding or removing anything.
So just drag the file into the GUI of MKVtoolnix and press “Start Muxing”.

@thirdgen89gta

Is there a way to locate the exact Media folder based on item ID, or info in the XML?

Unfortunately this is not as straightforward.
I think Home · WebTools-NG/WebTools-NG Wiki · GitHub can give you a hint about the location of the metadata bundle if you use the highest detail level for export.

[thirdgen89gta]

Sure, I’ll send it through MKVToolnix again and see if that resolves it.

[OttoKerner]

Don’t forget the Plex Dance afterwards.

[thirdgen89gta]

Unfortunately Cmdr Heatherly called “no joy”, and went below the hard deck. Thanks for the suggestion about Remuxing it though.

It would be nice to figure out why it doesn’t generate thumbnails, even if its not something easily fixed. Its only one file that does it, so I guess I’ll have to learn to live without them.

1. Removed the file from the media library
2. Scanned library to remove from library.
3. Plex Dance (trash, optimize, cleaned bundles)
4. Stopped, Started Plex service
5. Re-added newly muxed file back to Movie folder.
6. Scanned library to force re-add it.

Same result, no thumbnails.

I think I remember reading something in another thread when searching about Key frames being missing, but I think that worked fine for chapter thumbnails, it was just the video thumbnails that were missing.

Longstanding bug with video preview thumbnail generation - easily reproducible

There is a very old bug in Plex which me and a few others reported about a year ago, regarding the generation of video preview thumbnails. This happens with certain titles that have an unusual encoding format. It’s very easy to reproduce. Take any Blu-ray or 4K disc published by the Arrow label. This is not confined to Arrow, but I know for a fact they all use the same GOP encoding. Rip the title to MKV using any method you prefer. Add it to a Plex library with video preview thumbnail generat…

Video Preview Thumbnail Generation Fails for Some Items

Okay, I think I’ve narrowed it down further and found the problem, in my case at least. When you encode to H264 format, you can choose to output as “Closed GOP” or “Open GOP”. GOP stands for “Group of Pictures” and it’s something to do with the way that various compression frames are arranged. Something like that… it’s too technical for me! As I understood it, “Closed GOP” files are meant to be used when you know you later want to edit the file, and then when you’re ready to output the final v…

[OttoKerner]

I think chapter thumbs are only added during a server maintenance period.

[OttoKerner]

I not sure, but it might currently not work during ingestion.

Does the XML already show references to thumbs?

[thirdgen89gta]

I have mine set to generate them during maintenance, and when ingested.

PMS is running on a TrueNAS Scale host in a Linux VM with 16 threads assigned to it from an EPYC 7443p 24 core CPU, and it has 10Gb ram assigned. I also have NVEnc HW Acceleration on it. So it has way more HP than needed. So it doesn’t have any issues with resources. But I do understand some people need to defer the generation to the maintenance period so it doesn’t clog up the server during normal hours. It just isn’t an issue for my setup.

[thirdgen89gta]

This is the updated XML after re-muxing. I do see references to ‘thumb’ in the XML text.

I should add that when I’m watching the GUI, I can see the progress notification that its ‘generating thumbnails’ for both Chapters and video, but the progress circle never starts at all.

Usually a 1080p video only takes about 1-3 minutes for a full length movie to complete the generation process, and I can visibly watch the circle complete.

In this movies instance, I see the entry, but the progress circle never even starts.

771430_ProjectAko3_afterremux.xml.txt (14.7 KB)

[OttoKerner]

Could you try to make a sample file of this movie
then add it to a test library and see if the chapter generation is still failing?
(this of course requires a chapter marker marker to be present in the shortened sample file)

Otherwise we’d have to send the whole video file to a developer for investigation.

[OttoKerner]

Do you have video preview thumbnails activated in this library as well?
And if so, do these appear and are not just black?

Here is another thing to try:
set the hidden preference GenerateBIFKeyframesOnly to 0
https://support.plex.tv/articles/201105343-advanced-hidden-server-settings/
Then stop and restart the server and repeat the Plex Dance with this movie.

[thirdgen89gta]

I could do that an export a sample. I’m familiar with CMDline work so running Plex transcoder manually shouldn’t be an issue.

I did search the log files for the item ID, and came up with two hits.

plexy@plexy:/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Logs$ grep "771433" *.log
Plex Media Scanner Analysis.2.log:Dec 21, 2022 10:26:05.073 [0x7fe18853db00] INFO - /usr/lib/plexmediaserver/Plex Media Scanner --analyze --log-file-suffix  Analysis --no-thumbs --item 771433
Plex Media Scanner Deep Analysis.3.log:Dec 21, 2022 10:34:15.262 [0x7f818a250b00] INFO - /usr/lib/plexmediaserver/Plex Media Scanner --analyze-deeply --item 771433 --log-file-suffix  Deep Analysis

plexy@plexy:/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Logs$ cat 'Plex Media Scanner Analysis.2.log'
Dec 21, 2022 10:26:05.073 [0x7fe18853db00] INFO - Plex Media Scanner v1.30.0.6486-629d58034 - Ubuntu PC x86_64 - build: linux-x86_64 - GMT -06:00
Dec 21, 2022 10:26:05.073 [0x7fe18853db00] INFO - Linux version: 22.04.1 LTS (Jammy Jellyfish), language: en-US
Dec 21, 2022 10:26:05.073 [0x7fe18853db00] INFO - Processor: 16-core AMD EPYC 7443P 24-Core Processor               
Dec 21, 2022 10:26:05.073 [0x7fe18853db00] INFO - /usr/lib/plexmediaserver/Plex Media Scanner --analyze --log-file-suffix  Analysis --no-thumbs --item 771433
Dec 21, 2022 10:26:05.215 [0x7fe18bebc140] WARN - [FFMPEG] - Could not find codec parameters for stream 3 (Subtitle: hdmv_pgs_subtitle (pgssub)): unspecified size
Consider increasing the value for the 'analyzeduration' (20000000) and 'probesize' (20000000) options
Dec 21, 2022 10:26:05.215 [0x7fe18bebc140] WARN - [FFMPEG] - Could not find codec parameters for stream 4 (Subtitle: hdmv_pgs_subtitle (pgssub)): unspecified size
Consider increasing the value for the 'analyzeduration' (20000000) and 'probesize' (20000000) options

plexy@plexy:/var/lib/plexmediaserver/Library/Application Support/Plex Media Server/Logs$ cat 'Plex Media Scanner Deep Analysis.3.log'
Dec 21, 2022 10:34:15.262 [0x7f818a250b00] INFO - Plex Media Scanner v1.30.0.6486-629d58034 - Ubuntu PC x86_64 - build: linux-x86_64 - GMT -06:00
Dec 21, 2022 10:34:15.262 [0x7f818a250b00] INFO - Linux version: 22.04.1 LTS (Jammy Jellyfish), language: en-US
Dec 21, 2022 10:34:15.262 [0x7f818a250b00] INFO - Processor: 16-core AMD EPYC 7443P 24-Core Processor               
Dec 21, 2022 10:34:15.262 [0x7f818a250b00] INFO - /usr/lib/plexmediaserver/Plex Media Scanner --analyze-deeply --item 771433 --log-file-suffix  Deep Analysis
Dec 21, 2022 10:34:15.386 [0x7f818dbcf140] WARN - [FFMPEG] - Could not find codec parameters for stream 3 (Subtitle: hdmv_pgs_subtitle (pgssub)): unspecified size
Consider increasing the value for the 'analyzeduration' (20000000) and 'probesize' (20000000) options
Dec 21, 2022 10:34:15.386 [0x7f818dbcf140] WARN - [FFMPEG] - Could not find codec parameters for stream 4 (Subtitle: hdmv_pgs_subtitle (pgssub)): unspecified size
Consider increasing the value for the 'analyzeduration' (20000000) and 'probesize' (20000000) options

[thirdgen89gta]

@OttoKerner

you have video preview thumbnails activated in this library as well?
And if so, do these appear and are not just black?

Here is another thing to try:
set the hidden preference GenerateBIFKeyframesOnly to 0
https://support.plex.tv/articles/201105343-advanced-hidden-server-settings/
Then stop and restart the server and repeat the Plex Dance with this movie.

I have made the changes GenerateBIFKeyframesOnly=“0” to the Preferences.xml file, and Plex-Danced.

I am now seeing CPU usage during generation, in addition to progress on the circle.

And after finishing, I now see both Chapter, and Video thumbnails.

So, it is likely a Keyframe issue.

[OttoKerner]

You might want to revert the change, now that the movie has its thumbs.
Or the higher CPU load will continue on future media ingestions.

[thirdgen89gta]

Higher CPU load isn’t really a concern to me, so I’ll keep it unless I start seeing issues. I’ll keep the changes I made in mind in case I do start noticing a slow-down or other odd behavior after adding lots of media (like a TV season)

I added LongRunningJobThreads=“16” to the Preferences.xml, and increased the hypervisor thread assignment from 16 threads, to 24.

Between the Nvidia HW Acceleration, and the sheer number of threads on the host system (24 core, 48 thread).

The other other competing VM that might cause a resource issue is Ripping VM which has 40 threads and 20GB of ram assigned to it. I use that VM for compressing special features to H265 with some custom settings to get the special features to between 20% to 30% file size.

My other VM’s for my Homelab AD environment don’t come anywhere near using enough thread count.