I believe the same cable is used to connect an iPod to a BMW car's audio system.
It also allows a simple USB stick containing music to be used instead of the cable/converter/iPod, saving a ton of money. The USB stick must contain music in .MP3 files and be be formated in FAT32 mode. I have a 64GB USB stick which is a USB3 standard, meaning it is very fast and came with FAT32 formatting.
Like most tech topics, there are a few hitches, which this post is intended to smooth out.
Many years ago I took my entire CD collection and digitized each one, creating a library. I forget if I used iTunes or not, I think I did. It is simple, but does not have full flexibility. In addition to it, I have Media Monkey and between the two, I have the flexibility I need.
I store my music "library" file in a place where I can always find it on my fast desktop Windows computer. Sorry, Apple computer users, not all I say here might be directly usable by you, but it still might help.
As you can see above, the Music folder contains more folders as shown on the right. All Music contains the songs, organized in a standard way used by both iTunes and Media Monkey. This is an industry standard, not invented by me. The folders and the order of items in the folders was done by whatever program I used long ago and still works fine today.
Looking into the All Music folder, you can see there is a folder for each artist, so we need to "drill down" a bit more.
For each artist, there is a folder for each album.
And, you can now see there is a .MP3 file for each song. .MP3 files may not be the highest fidelity files, but since they are required for use on the RT, I use them.
Now we will talk about PLAYLISTS. The word itself seems to have multiple meanings
The first is a non-technical and obvious meaning, referring to two or more songs played in a certain order on a DJ's radio show for example.
But, most programs like iTunes and Media Monkey and most devices like iPods or your smartphone music app(s) will make a playlist for you so you can be your own DJ and make a list of songs you want played under different circumstances that suit you. For the USB stick, you need to create the most common type of playlist, one with a filename ending in .M3U. This is usually the default type anyhow.
After moving the music and the playlists to the USB stick, you can search the stick for for *.M3U files. Opening one of these using Notebook, you will see something that looks like:
For those of you who know about file system "paths", you will see this file is a set of pointers that allows each song to be found on the USB stick by the computer that is in the sound system.
If it does not look like this, and the sound system display says something like "no data", it means that the playlist file was not made correctly. I have made a few like that myself, because I did not really understand how to use Media Monkey correctly. Eventually, I read the help file and used the generiic USB stick addin. You might be able to avoid this. It happened to me when I had a slightly messed up music library, which took effort to fix. All is well now. Hopefully you will be ok.
Media Monkey and many other music player applications have the ability to convert music files from other formats to .MP3 formats. See the Help files for how to do this in your program. Also, to find missing files, etc. and clean up a messed up music library.
I hope this helps some folks. I am going to post a message to my fellow BMW MOA members as some of them will be interested.