To convert an .mscz file to MIDI reliably, the official and most verified method is using MuseScore Studio directly. Since .mscz is the native format for MuseScore, the software handles the conversion with the highest accuracy for note data and tempo. Official Conversion Steps
Troubleshooting
If the conversion doesn't seem accurate, check the original MSCZ file for any issues or complexities that might not have been correctly translated.
Ensure you're using the latest version of music21, as updates may improve conversion accuracy.
: For those comfortable with the command line, MuseScore supports a Converter Mode . You can run mscore -o output.mid input.mscz convert mscz to midi verified