I am using Debian Bullseye and already for a long time I noticed that Nautilus failed to generate thumbnails for certain video files, leading to only a generic video icon instead of a thumbnail.
In the kernel log (dmesg), you will see this error:
qtdemux0:sink: segfault at 0 ip 0000000000000000 sp 00007f724fe61d18 error 14 in totem-video-thumbnailer[5638abe9b000+3000]
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
This is Debian bug #967941: gnome-video-thumbnailer crashes with a segmentation fault when thumbnailing H.264 encoded video files when you have the package
# apt-get remove libopenblas0-pthread
This might not be possible if you need this package for other reasons.
For performance reasons you might also want to install the BLIS BLAS implementation and set it as default. Install the packages
libblis64-3-pthread and set them default using the update-alternatives commands from the next work-around.
Switch the default BLAS implementation from OpenBlas to Atlas
If you cannot uninstall libopenblas0-pthread, you can change the default BLAS and LAPACK implementation on your system to a different implementation than OpenBLAS
# update-alternatives --config libblas64.so.3-x86_64-linux-gnu
# update-alternatives --config libblas.so.3-x86_64-linux-gnu
# update-alternatives --config liblapack.so.3-x86_64-linux-gnu
Choose a different implementation than openblas in all 3 cases. Usually Atlas will be installed and available by default. You can also install the packages
libblis64-3-pthread and choose the BLIS implementation for the former two and Atlas for the latter.
Disable the sandbox in totem-video-thumbnailer
Totem-video-thumbnailer uses some kind of sandbox limiting how much CPU and memory resources the process can use. This enhances security and prevents the process from using all resources in case something would go wrong. OpenBLAS causes problems in combination with these restrictions. You can disable them in totem-video-thumbnailer by calling it with the
-l option. To automatically let GNOME call it with that option, edit the file
/usr/share/thumbnailers/totem.thumbnailer and edit the Exec= line so that it looks like this:
Exec=/usr/bin/totem-video-thumbnailer -l -s %s %u %o
If you can, rather use one of two previous work-arounds, because disabling this restrictions could have security implications.
Regenerating the failed thumbnails
Finally after implementing one of the 3 work-arounds, you will need to regenerate the failed thumbnails. GNOME Thumbnail Factory keeps a list of all failed thumbnails, so that it does not retry to generate them over and over again. They are stored in
~/.cache/thumbnails/fail/gnome-thumbnail-factory so you can just delete this directory:
rm -rf ~/.cache/thumbnails/fail/gnome-thumbnail-factory
Now when you browse a directory which contains video files with missing thumbnails with Nautilus, it should generate them automatically.