AVformat missing

I made several more attempts, but without success
It very strange this behaviour because Kdenlive stop itself to work some days ago.
Is possible that the problem is some software update of Ubuntu ?

Looks like you have several versions of MLT installed. Suna's repository installs the "melt" executable in /usr/bin/melt, but your screenshot shows that you have melt installed in /usr/local/bin.

So you must have installed melt by another way before. You should remove all MLT stuff in /usr/local, then it should work.

You must make sure to remove all MLT files in /usr/local.

Make sure to remove:

/usr/local/lib/libmlt*
/usr/local/lib/mlt/
/usr/local/share/mlt
/usr/local/lib/pkgconfig/mlt*

Then remove the Kdenlive config file:

$HOME/.kde/share/config/kdenliverc

and restart Kdenlive

To add to the thread:
I had exactly the same problem like antonvdh on (a very old installation of) Debian Sid. MLT was missing the avformat producer and Kdenlive was reporting missing FFMPEG, without reporting any broken libraries. Besides this I also had other symptoms like segfault in postinst script of vlc-nox package and strange things happening with Nvidia binary driver.

What I did was purge my /etc/ld.so.conf of entries that have accumulated there during the years. The file now only inlcudes the .conf files in /etc/ld.so.conf.d and after a ldconfig everything works now.