Hahahahahaha. My solution is not cheap and its kinda a big process. Still debating if it was really worth it.

I had hundreds of thousands of midi files to convert.

I used GNMIDi pro and I had the developer write a add on tool that would mass convert midi files into progressions.

Gnmidi pro is 49 dollars and the extra tool is 20 euros.

The caveats are it does not detect key so you have to have all your midi files by key/scale separated in folders. It doesn't detect chords names. in the chords name field it will put just the notes in the chord i.e A#,C, E. It always sets the chords as Normal. In order to change these in bulk you need another script to mass edit the progression files.

It works by taking the note on data and ignoring the note off data.

This means all your chords need to be quantized and there cannot be any overlaps. i did bulk editing of files in Studio One which is a breeze with macros.

Once your files are prepped you batch convert . You set the key and scale in the initial options then it writes the progression files very quickly.

The problem is that you need to use a batch editor to do search and replaces for chord names and which chord is the root. If you have programming skills you could write an algorithm to replace the note group with chord names.

I don't have those level of skills so I used a chord table that i made from every possible scaler chord (actually still working on that) and then used Gillmeister batch text replacer $50 to replace chord names and find and set the root chord.

I've done most of the hard work so it shouldn't be as hard or as long for anyone else to do this using my method (and the batch text replacer profile i wrote) but it still costs$$$$. Im thinking about just selling the progressions as pack once Im finished because it may not be worth alot of peoples time and money to do it the way i went.

And it cost me way more money than I wanted to spend because I tried a few other solutions as well but this solution once your prep is done can convert thousands of files at a time in minutes with a few button clicks.