Thumbnails periodically get reset, only seems to happen with WEBM files

[billcw 2]

I have a bunch of WEBM TV episodes with thumbnail attachments.  When I first add them, Emby uses the attachments for the thumbnail as expected.  But sometime later, they will get reset to the season thumbnail.  At that point, the only way to reset the thumbnails is to remove the episodes from the library completely and add them again.  Attempting to refresh the metadata with images does not change anything.  I never had this experience with MKV files.  I don't know if I am doing something to trigger this or if it is happening automatically.  Any ideas?

[Luke 42077]

Hi there, can you please show a specific example? Thanks !

[billcw 2]

Sure.  Here is what it looks like when freshly added:

And here is what it looks like a day or two later:

[billcw 2]

I don't know what was going on, but it seems to have resolved itself.  Refreshing the metadata started to work again, restoring the images.  I guess we'll have to wait to see if it lasts.

[Luke 42077]

Hi, thanks for following up.

[billcw 2]

I figured it out!  I add PNG thumbnails to the WEBM files.  Then, I normally move them to a .images subdirectory in case I need them again later.  If, instead, I forget and leave the images in the same directory with the video files and then try to refresh the metadata, I get the season thumbnail as shown in the images above.  As soon as I move the images out of the same directory, it works as expected.

[Luke 42077]

What are all of the file names involved?

[billcw 2]

The thumbnail filenames are the same as the video, but with a PNG extension.  For example, "Death Valley Days S01E01 - 1080p.webm" and "Death Valley Days S01E01 - 1080p.png".

[Luke 42077]

is your png thumbnail the black and white image?

[billcw 2]

Yes, that's right.

[Luke 42077]

@Happy2Playare you able to reproduce?

[Happy2Play 9780]

On 5/26/2025 at 4:50 PM, billcw said:

The thumbnail filenames are the same as the video, but with a PNG extension.  For example, "Death Valley Days S01E01 - 1080p.webm" and "Death Valley Days S01E01 - 1080p.png".

So the issue is .webm images eventually get replaced correct?

@Lukeis there full support for .webm images?

KB

Quote

Supported image extensions are jpg, jpeg, png, gif and tbn.

 

[billcw 2]

Now that I understand how Emby works, I'm not sure if it is worth the time to fix this problem, as I doubt that many people will run into it, but here is a sequence of screenshots to illustrate.  I ran refresh metadata with image replacement in between each step.  Everything works as expected except in case 3, where Emby produces a default thumbnail when it has two options for the custom thumbnail.

Case 1 (No custom thumbnails)

Thumbnail png files: No

Thumbnail webm attachments: No

Emby generates a default thumbnail for the episodes, as expected.

Case 2 (Thumbnails in separate images files)

Thumbnail png files: Yes

Thumbnail webm attachments: No

Emby uses the png thumbnails as expected.

Case 3 (Thumbnails both as image files and as webm attachments)

Thumbnail png files: Yes

Thumbnail webm attachments: Yes

You can see the webm attachment in the mkvmerge listing and the png files in the directory.  Emby uses the default, season thumbnail, which seems unexpected.

Case 4 (Thumbnail as webm attachment only)

Thumbnail png files: No

Thumbnail webm attachments: Yes

I have now moved the png thumbs out of the directory but left the attachments in the webm files.  Emby uses the expected thumbnail.

[Happy2Play 9780]

Think I miss understood the issue here.

Does webm even support attachments?

The WebM Project | WebM Container Guidelines

[Happy2Play 9780]

But attached image to this test file

C:\Users\Media>C:\Users\Media\AppData\Roaming\Emby-Server\system\ffprobe.exe -i E:\Media\Photo2\big-buck-bunny\big-buck-bunny.webm
ffprobe version 5.1-emby_2023_06_25_p4 Copyright (c) 2007-2022 the FFmpeg developers and softworkz for Emby LLC
  built with gcc 12.2.0 (Rev10, Built by MSYS2 project)
Input #0, matroska,webm, from 'E:\Media\Photo2\big-buck-bunny\big-buck-bunny.webm':
  Metadata:
    encoder         : http://sourceforge.net/projects/yamka
    creation_time   : 2010-05-20T08:21:12.000000Z
  Duration: 00:00:32.48, start: 0.000000, bitrate: 537 kb/s
  Stream #0:0(eng): Video: vp8, yuv420p(progressive), 640x360, SAR 1:1 DAR 16:9, 25 fps, 25 tbr, 1k tbn (default)
  Stream #0:1(eng): Audio: vorbis, 44100 Hz, mono, fltp (default)
  Stream #0:2: Video: mjpeg (Baseline), yuvj420p(pc, bt470bg/unknown/unknown), 250x141 [SAR 100:100 DAR 250:141], 90k tbr, 90k tbn (attached pic)
    Metadata:
      filename        : cover.jpg
      mimetype        : image/jpeg

put in home video library

2025-06-30 12:05:25.985 Info SingleImageExtractor: ProcessRun 'extract-image' Execute: C:\Users\Media\AppData\Roaming\Emby-Server\system\ffmpeg.exe -i file:"E:\Media\Photo2\big-buck-bunny\big-buck-bunny.webm" -map 0:2 -threads 0 -vf "thumbnail=24" -f image2 -b:v 100M "C:\Users\Media\AppData\Roaming\Emby-Server\programdata\cache\temp\d97cae43-294f-4123-a859-a275ddf77a88.jpg"
2025-06-30 12:05:25.998 Debug SingleImageExtractor: ProcessRun 'extract-image' Started.
2025-06-30 12:05:26.093 Info SingleImageExtractor: ProcessRun 'extract-image' Process exited with code 0 - Succeeded
2025-06-30 12:05:26.508 Info ProviderManager: Saving image to C:\Users\Media\AppData\Roaming\Emby-Server\programdata\metadata\library\07\07798aa33d41c46403297c6c6f40c6a4\poster.jpg

 

Do have you verified your images options on the library?

 

Only tested on 4.9.1.3

Edited June 30, 2025 by Happy2Play
added server test version

[billcw 2]

Perhaps webm attachments should be ignored by Emby if they are unsupported, but they work reliably for me.  (I assume Emby just treats webm files as mkv, as many players seem to, since it also allows things like multiple audio tracks, which is clearly not allowed.)  However, I'm guessing that you would find that a lot of people are using webm thumbnails if you decided to ignore them.

Only the case where Emby has two options: both an external png image and a webm attachment, at the same time, doesn't work and perhaps the right fix for that is just documentation.

From the outside, it seems like the ideal solution would be that Emby just ignores any other thumbnail options if an external image file exists.

Edited June 30, 2025 by billcw

[Happy2Play 9780]

5 hours ago, billcw said:

From the outside, it seems like the ideal solution would be that Emby just ignores any other thumbnail options if an external image file exists.

Guess I am confused as that is what Emby does.  If any correctly named image exists with media it will be used.  Local images will always superseded getting from online or extracting.

What is your library image settings?

I will have to setup a Series to test this as I can reproduce any issue with a movie.

[Luke 42077]

So what you're seeing is the image that's embedded inside the webm file?