tlmb - The Little MusicBox - audio/video player, Qt6 based using mpv for playing audio/video files

In a living room, tlmb is meant to be used with a TV.
There are 3 play modes: single song, to end of song list and loop through list.
It provides an easy way to control a music file collection with a remote keyboard.
Basically a special type of file manager optimized to easily play music files.
But for this tlmb requires and expects a special structure of the music files.

The required stucture/level:
- A root directory:
- Music type directories under the root directory: e.g. classic, non-classic, bluez, jazz, etc.
- artist/band directories fore each music type directory
- songs in each artist/band directory

An example:
- rootdir/
- rootdir/classic/LeaDesandre/A_Chloris
- rootdir/classic/LeaDesandre/Scheraz_Infida
- rootdir/classic/MariSamuelsen/Richter-Dona_Nobis_Pacem_2
- rootdir/non-classic/BlackDub/I_Believe_In_You
- rootdir/non-classic/BlackDub/May_Be_The_Last_Time
- rootdir/non-classic/Sia/Elastic_Heart
- rootdir/non-classic/Sia/Chandelier

tlmb uses mpv to play the music files. mpv is started as a standalone player, not under the control of tlmb.
This allows playing pure audio files as well as music videos and the users mpv configuration file will be used.
While playing, mpv can be controlled by it's usual key/remote commands.
As mpv is used as the player, tlmb is more targeted for playing music video, but will play pure audio files just fine.

Playlists following the *.m3u standard are supported
They can be set to be played from for each level and to add songs to them. It is also possible to create new add-to playlists for each level.

To support multiple CDs per artist/band, you could either choose to create multiple directories per artist/band:
artist_band_CD1 and artist_band_CD2
or store all files in artist_band/ and use (a) playlist(s) to select your favorites to play from all songs from this artist/band.
Multiple playlist per artist/band are supported, so you could add a playlist per CD and another for your favorite playlist across all song from all CDs of this artist/band.

It is also possible to create playlists across multiple artist/bands per music type and across everything on the root level:
any music type and any artist/bands: e. g. female_voices from music type non classic (or pop, whatever your selection is) and classic.

Right-click on a song to add it to the add-to playlist, indicated by the green cross.
Right-click on a play-from playlist combobox to open an editor to edit the playlist: change the order or drop a song from it.
Right-click on an add-to playlist combobox to either create a new, rename an existing or save the current playlist under a new name or to edit the current add-to playlist: change the order or drop a song from it.

The program is released under the MIT license.

The tlmb main screen.
The shown songs to play are from the artist/band directory, indicated by the blue note.
Songs will be added to the 'nonclassic-mix4.m3u' playlist, indicated by the green plus.

The settings dialog. Not all functions are currently implemented, e. g. the font setting is still a placeholder:

tlmb does not have any useful command line options. When invoked with an option, a (short) help message will be printed on standard out.
Start the program without any command line option.
The root directory holding the tlmb music structure can be set via the settings dialog, accessible via the menu or Ctrl+s.
Read more in the online help, accessible from the menu.

Requirements:
- Qt6 (including development files)
- cmake (build tool)
- mpv (not required for compiling tlmb, but to play audio/video files)