Ext4 is a filesystem. That is the part of the kernel that actually stores and retrieves the files on disk. What program are you using to browse files? It’s a bit hard to tell from this screenshot what program it’s a screenshot of, but it looks like Nautilus (the default file browser in GNOME). Is that it?
You have openh264 installed already which should cover your bases. Since it quite clearly isn’t I’m not sure what to suggest. What file manager is this that’s having issues?
And here are instructions from a third party explaining how to tell apt how to install them so they can be kept up to date (be sure you read the warning on the debian.org page about why they don’t tell you to do that before you do it):
Depending on how exactly your file manager works, installing the codec may or may not be sufficient to display thumbnails. If not, there are probably instructions specific to your file manager for installing the appropriate plugin.
ffprobe is included in the ffmpeg package. For future reference you can find what package contains a file by doing dpkg-query -S /bin/ffprobe (note that the path you give it is relative to /usr)
Every time I commit I have to look through git diff, figure out what the hell I actually did, come up with something intelligent to say about jt, possibly split the commit into multiple commits if I changed multiple things, do some shuffling with git reset and git add…
For some reason all my personal projects are all like 4K SLoC with 50 total commits, all of which include apologies for not doing more smaller commits