Bug 500117

Created attachment 178394 [details]
2 video files whose thumnails show only the backdrop (background) images even though the poster image has been embedded too.

SUMMARY
Integrated (embedded) poster images in Matroska (.mkv) video files are not shown in the main view (content area) as long as other images files also exist inside the file

STEPS TO REPRODUCE
1. Open in Dolphin a folder where you have a  video / movie that has both a poster (cover) and a backdrop (background) artworks integrated (embedded) into it.
2. If you don't have such a file, follow these steps (inside the dashes):
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1. Find a Matroska (.mkv) file on your computer or download one from sample pages like:
https://sample-files.com/videos/mkv/
https://thetestdata.com/sample-mkv-file-download.php
2. Take a poster from here (Menu: Media -> Posters):
https://www.themoviedb.org/movie/10378-big-buck-bunny/images/posters
And a backdrop (background image) from here (Menu: Media -> Backdrops):
https://www.themoviedb.org/movie/10378-big-buck-bunny/images/backdrops
3. Save (or rename after you downloaded) the poster image as: 'cover.jpg' and the backdrop image as: 'cover_land.jpg'.
As this page tells:
https://www.matroska.org/technical/attachments.html
4. Download, install and open MKVToolnix
https://mkvtoolnix.download/
On Debian: sudo apt install mkvtoolnix-gui
5. Drag the prepared .mkv file into the "Source files:" field of the "Input" tab of MKVToolnix.
6. Switch to the "Attachments (0)" tab.
7. Drag the prepared cover.jpg and cover_land.jp files into the "Attachments to add:" field (Untick / uncheck files in the Attachments from source files:, if any).
8. Click on the "Start multiplexing" button at the bottom.
9. Switch to the "Job output" on the left vertical panel.
10. Click on the "More actions" button at the bottom and them on the "Open folder"
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3. Look at the file in the main view (content) area of Dolphin (enable previews - F12, if they are not enabled aready).

OBSERVED RESULT
For all view modes (icons, compact and details) the thumbnail doesn't show the poster (cover.jpg) preview embedded (integrated) in the .mkv file.
As long as a backdrop / background (cover_land.jpg) image has been embedded too.
If I remux the file with MKVToolnix to not include the backdrop (cover_land.jpg) image also, then then the file thumbnail shows the poster.
It's like it's looking for a single image to be embedded and it displays that.
If there are more, than it takes the second.

EXPECTED RESULT
I expect to see the poster (cover.jpg) embedded in the .mkv file, even if a backdrop / baground (cover_land.jpg) file was also embedded. 

Since the backdrops (background) images most of the times don't have any texts on them or are just some frames (captures) from the videos are way less helpful than the posters for recognizing what the video is about.
The priority for showing art works should be the posters first and backdrops only if the posters doesn't exist.

I also expect that I don't have to download and install MKVToolnix, to remove art works from my files so that the poster can be shown.
I pretty much put both the poster and the backdrop to all the files that I mux / remux with MKToolnix.
Some other software is able to show in its interface both the poster and the backdrop as a background so I want that my .mkv files have everything they need embedded into them.

If in the future I will add for embedding more image files, let's say other types of artworks or posters + backdrops in other languages, which are not part of the poster / backdrop standard, but you are allowed to add them, the poster should still work (be read and displayed).
If the poster doesn't have the .jpg extension, but .png or other standard, it should still work.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma:
KDE Plasma Version: 6.3.0
KDE Frameworks Version: 6.10.0
Qt Version: 6.7.2
Kernel Version: 6.12.13-amd64 (64-bit)
Graphics Platform: Wayland

HARDWARE SPECIFICATIONS
Hardware: Laptop Dell Inspiron 5770 (17" 1080p@60Hz screen)
CPU: Intel® Core™ i5-8250U CPU @ 1.60GHz
GPU 1: Mesa Intel® UHD Graphics 620 (main)
GPU 2: AMD Radeon R5 M465 Series
RAM: 8 GiB (7.7 GiB usable)

ADDITIONAL INFORMATION
On Windows, the Icaros tool (part of the K-lite codec pack) does a similar thing:
https://www.videohelp.com/software/Icaros
And when I was using it on Windows 7, it always preferred to show the posters, if they were embedded.
If they were not, then it showed a frame from somewhere in the video file.
When both the poster and the backdrop were present, then it preferred to show the poster image.

BTW, I created a similar report for the 'Information' panel, that also shows only the backdrop when both artworks are available, even though it has enough vertical space to actually show both of them :
https://bugs.kde.org/show_bug.cgi?id=500113