Bug 406515

SUMMARY
This is almost a re-edition of bug #400264, but neither a re-opening nor a duplicate. This one can be easily avoided with a simple correction to the documentation and fixed with a simple step (see below). The first most important part is the "how to avoid" this problem from keep reappearing. The second important thing is how to fix it, see Additional Information below.

Issue:
In Ubuntu 18.04 is not possible to install (or update to) kdenlive 18.12.3+git201902280143~ubuntu18.04.1 using the official ppa:kdenlive/kdenlive-stable, because required libraries libmlt++3 and libmlt6 in that PPA are too old.

STEPS TO REPRODUCE
1. In ubuntu 18.04, install -if never done before- the Kdenlive official ppa:kdenlive/kdenlive-stable, then sudo apt update.
2. sudo apt install kdenlive # OR sudo apt install --reinstall kdenlive if existing installation of previous version.

OBSERVED RESULT
Error is returned:
The following packages have unmet dependencies:
 kdenlive : Depends: libmlt++3 (>= 6.13.0+git201903302059~ubuntu18.04.1) but 6.10.0+git201810170323~ubuntu18.04.1 is to be installed
            Depends: libmlt6 (>= 6.13.0+git201903302059~ubuntu18.04.1) but 6.10.0+git201810170323~ubuntu18.04.1 is to be installed
E: Unable to correct problems, you have held broken packages.

EXPECTED RESULT: Successful installation/upgrade, no error messages.

ADDITIONAL INFORMATION

1) First, the _second_ most important thing: how an user can fix this problem (officially). If you have this issue, please add one more PPA with this command:

sudo add-apt-repository ppa:kdenlive/mlt && sudo apt update

With the official mlt PPA, now you should have access to the up-to-date libraries that are missing in ppa:kdenlive/kdenlive-stable, so you should now be able to install or upgrade kdenlive to 18.12.3+git201902280143~ubuntu18.04.1.

2) Finally, the most important thing: How to avoid this issue from hitting less experienced users. This is a job for the Kdenlive team, and it is very simple.

Dear Kdenlive Team:

Please, can you fix the instructions in the https://kdenlive.org/en/download/ web page, section
"GNU/Linux Packages -> Ubuntu | LinuxMint | Elementary"

Currently, and since a couple of years already, it states:

"It is recommended to download the AppImage version until the release of Ubuntu 18.04."

That sentence has at least two problems:

First, it is obsolete because Ubuntu 18.04 has been released since... well, 2018-04. This could be understood as "at this point in time it is OK to use ppa:kdenlive/kdenlive-stable". But...

Second: It IS actually OK to use that PPA. But unless you are a magician and guess that there is hidden secret to it in https://community.kde.org/Kdenlive/Development#Pre-requisites_and_Supported_Platforms, you are in for a ride that could bring you to read this bug report or perhaps to write another one similar to it.

SOLUTION:
The solution is very simple: Fix the Kdenlive website, by remove misleading/obsolete information about Kdenlive installation and replace it with a pointer to a SINGLE, up-to-date source of information.  Sounds complicated, but it is not.  I suggest this:

Please replace the above mentioned incorrect/misleading sentence in
https://kdenlive.org/en/download/ web page, section "GNU/Linux Packages -> Ubuntu | LinuxMint | Elementary"
and replace it with something like this:

"It is recommended to download the AppImage version. If you prefer the convenience of our PPA, please refer to these instructions: https://community.kde.org/Kdenlive/Development#Pre-requisites_and_Supported_Platforms."

Voilá !

You get the idea. Make that obscure link much more visible (why don't you give it a better, more explicit title/subtitle about "Installing via PPA"?) and do not write contradictory/easy to expire/duplicated information elsewhere, just links to the only place which is correct and updated.

Something like that should free you from having to maintain more than one place with download/installation instructions. So far, you have at least two bug reports (from my self) on this issue, plus many unnecessary complaints and discussions.

This is a Documentation problem that generates Installation problems, and the impact on Installation is bigger and exactly what the user will perceive and rant about in the first place. That's why I filed an Installation bug, although this might generate philosophical argumentation (please don't).