Trying to install YouTube To MP3 application on Ubuntu 18.04 which works on my Ubuntu 16.04 without problems.
When I double-click on the deb file, it runs GUI installer but when I click on install, it starts to install, then stops and show no errors but the install button is still there. 
So I try to install it manually, but there are errors too. I'll show you here my steps:
milano@milano-PC:~/Downloads$ sudo dpkg -i youtube-to-mp3-converter3-9-4-64-bit.deb
[sudo] password for milano:
Selecting previously unselected package youtube-to-mp3.
(Reading database ... 179031 files and directories currently installed.)
Preparing to unpack youtube-to-mp3-converter3-9-4-64-bit.deb ...
Unpacking youtube-to-mp3 (3.8.4) ...
dpkg: dependency problems prevent configuration of youtube-to-mp3:
youtube-to-mp3 depends on libqt4-declarative (>= 4:4.8.1-0ubuntu4.6); however:
Package libqt4-declarative is not installed.
youtube-to-mp3 depends on libav-tools; however:
Package libav-tools is not installed.
dpkg: error processing package youtube-to-mp3 (--install):
dependency problems - leaving unconfigured
Processing triggers for hicolor-icon-theme (0.17-2) ...
Processing triggers for gnome-menus (3.13.3-11ubuntu1.1) ...
Processing triggers for desktop-file-utils (0.23-1ubuntu3.18.04.1) ...
Processing triggers for mime-support (3.60ubuntu1) ...
Errors were encountered while processing:
youtube-to-mp3
So the problem is that it doesn't have dependencies installed:
milano@milano-PC:~/Downloads$ sudo apt-get install libqt4-declarative
Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
libqt4-declarative : Depends: libqt4-network (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
Depends: libqt4-script (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
Depends: libqt4-sql (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
Depends: libqt4-xmlpatterns (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
Depends: libqtcore4 (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
Depends: libqtgui4 (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
youtube-to-mp3 : Depends: libav-tools but it is not installable
Recommends: libav-tools-links but it is not installable
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).
So I do:
milano@milano-PC:~/Downloads$ sudo apt --fix-broken install
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following packages will be REMOVED:
youtube-to-mp3
0 upgraded, 0 newly installed, 1 to remove and 54 not upgraded.
1 not fully installed or removed.
After this operation, 1 434 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 179077 files and directories currently installed.)
Removing youtube-to-mp3 (3.8.4) ...
Processing triggers for mime-support (3.60ubuntu1) ...
Processing triggers for desktop-file-utils (0.23-1ubuntu3.18.04.1) ...
Processing triggers for gnome-menus (3.13.3-11ubuntu1.1) ...
Processing triggers for hicolor-icon-theme (0.17-2) ...
EDIT:
Try to install dependencies again:
milano@milano-PC:~/Downloads$ sudo apt-get install libqt4-declarative
Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
libqt4-declarative : Depends: libqt4-network (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
Depends: libqt4-script (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
Depends: libqt4-sql (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
Depends: libqt4-xmlpatterns (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
Depends: libqtcore4 (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
Depends: libqtgui4 (= 4:4.8.7+dfsg-7ubuntu1) but it is not going to be installed
youtube-to-mp3 : Depends: libav-tools but it is not installable
Recommends: libav-tools-links but it is not installable
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).
Then, when I try to install the app again, the first step happens again.
milano@milano-PC:~/Downloads$ sudo dpkg -i youtube-to-mp3-converter3-9-4-64-bit.deb
Selecting previously unselected package youtube-to-mp3.
(Reading database ... 179031 files and directories currently installed.)
Preparing to unpack youtube-to-mp3-converter3-9-4-64-bit.deb ...
Unpacking youtube-to-mp3 (3.8.4) ...
dpkg: dependency problems prevent configuration of youtube-to-mp3:
youtube-to-mp3 depends on libqt4-declarative (>= 4:4.8.1-0ubuntu4.6); however:
Package libqt4-declarative is not installed.
youtube-to-mp3 depends on libav-tools; however:
Package libav-tools is not installed.
dpkg: error processing package youtube-to-mp3 (--install):
dependency problems - leaving unconfigured
Processing triggers for hicolor-icon-theme (0.17-2) ...
Processing triggers for gnome-menus (3.13.3-11ubuntu1.1) ...
Processing triggers for desktop-file-utils (0.23-1ubuntu3.18.04.1) ...
Processing triggers for mime-support (3.60ubuntu1) ...
Errors were encountered while processing:
youtube-to-mp3
Do you know what to do?
EDIT
milano@milano-PC:~/Downloads$ sudo apt install libav-tools
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package libav-tools is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
ffmpeg:i386 ffmpeg
E: Package 'libav-tools' has no installation candidate
I have tested the deb-file from the linked site - it is version 3.9.4 (64-bit) and dated 04.05.16. So it expected to work on Ubuntu 16.04 LTS (not 18.04 LTS).
You can get newer version 3.9.9.5 from the developer's (MediaHuman) repository:
Then you can use it: