Batch midi transposer (with unresolved issue)

[ctrl-shift-ale]

Hi everyone, I have built a little app which allows to quickly transpose a batch of midi files to a range of transpositions.
The core algorithm is quite basic: the source midi file is copied as it is, and the note paramaters of the note_on and note_off messages are changed according to the transposition value.
For some reason though, the exported midi files play at a different tempo, and the overall duration of the track heppen to be either briefer or incredibly longer (like 20x the original or so).
I would be grateful if anyone could help me understanding what's the issue.
Thanks in advance.

#written by Alessandro Quaranta , July of 2023

from mido import MidiFile
from tkinter import *
from tkinter import filedialog as fd
import os

noteOffset = 0
folderIN = ""
folderOUT = ""
filesIn = []

suffices = ["C0","C#0","D0","D#0","E0","F0","F#0","G0","G#0","A0","A#0","B0",
			"C1","C#1","D1","D#1","E1","F1","F#1","G1","G#1","A1","A#1","B1",
			"C2","C#2","D2","D#2","E2","F2","F#2","G2","G#2","A2","A#2","B2",
			"C3","C#3","D3","D#3","E3","F3","F#3","G3","G#3","A3","A#3","B3",
			"C4","C#4","D4","D#4","E4","F4","F#4","G4","G#4","A4","A#4","B4",
			"C5","C#5","D5","D#5","E5","F5","F#5","G5","G#5","A5","A#5","B5",
			"C6","C#6","D6","D#6","E6","F6","F#6","G6","G#6","A6","A#6","B6",
			"C7","C#7","D7","D#7","E7","F7","F#7","G7","G#7","A7","A#7","B7",
			"C8","C#8","D8","D#8","E8","F8","F#8"]

root = Tk()
root.geometry("500x200")
root.title("")

def sel_folderIN():
	global folderIN
	global folderOUT
	folderIN = fd.askdirectory()
	print("Import Folder: ", folderIN)

	Label_FoldIN.config(text=folderIN)
	if folderOUT == "":
		folderOUT = folderIN
	Label_FoldOUT.config(text=folderOUT)

def sel_folderOUT():
	global folderOUT
	global folderIN
	folderOUT = fd.askdirectory()
	print("Export Folder: ", folderOUT)
	Label_FoldOUT.config(text=folderOUT)
	if folderIN == "":
		folderIN = folderOUT
	Label_FoldIN.config(text=folderIN)

def run():
	check_batch_folder()

	if len(filesIn) > 0:
		if int(Spbx_offsetFrom.get()) > int(Spbx_offsetTo.get()):
			offsetFr = int(Spbx_offsetTo.get())
			offsetTo = int(Spbx_offsetFrom.get())
		else:
			offsetFr = int(Spbx_offsetFrom.get())
			offsetTo = int(Spbx_offsetTo.get())

		fOut = ""
		# ~~~ parse imported midi files
		for fIn in filesIn:
			print("file is: ", fIn)
			for offset in range(offsetFr, offsetTo+1):
				if offset != 0:
					print("offset is: ", offset)
					# ~~~ generate name of the midi file to export
					idx = 0
					found = False
					for s in suffices:
						pos = fIn.rfind(s)
						if pos != -1:
							found = True
							if idx+offset >= 0 and idx+offset < len(suffices):
								pos = fIn.rfind(s + ".mid")
								if pos != -1:
									print("case 1")
									fOut = fIn[0:pos] + suffices[idx+offset] + ".mid"
								else:
									print("case 2")
									fOut = fIn[0:-4] + "_to_" + suffices[idx+offset] + ".mid"
							else:
								if idx + offset < 0:
									print("WARNING: the export note is lower then C0")
								else:
									print("WARNING: the export note is higher then F#8")
							break
						idx+=1
					if not found:
						if offset > 0:
							print("case 2")
							fOut = fIn[0:-4] + "_+" + str(offset) + ".mid"
						else:
							print("case 3")
							fOut = fIn[0:-4] + "_" + str(offset) + ".mid"
					print("File source " , fIn , " will be renamed as " , fOut)

					# ~~~ edit imported midi file
					midIn = MidiFile(folderIN + "/" + fIn, clip=True)
					midOut = MidiFile()
					for track in midIn.tracks:
						print(track)
						for msg in track:
							if msg.type == 'note_on' or msg.type == 'note_off':
								print("original note: ", msg.note)
								msg.note = msg.note + offset
								print("edited note: ", msg.note)
						midOut.tracks.append(track)
					print("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~")
					print("~~~~~~~ CHECK MIDI OUT FILE ~~~~~~~~")
					print("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~")
					for track in midOut.tracks:
						print(track)
					midOut.save(folderOUT + "/" + fOut)
	else:
		print("ERROR: NO SOURCE MIDI FILES FOUND")
def check_batch_folder():
	global filesIn
	filesIn = []
	files = os.listdir(folderIN)
	for f in files:
		if f.lower().endswith('.mid'):
			filesIn.append(f)
			print("FOUND FILE IN FOLDER: ",f)

root.columnconfigure(0, weight=10)
root.columnconfigure(1, weight=30)
root.columnconfigure(2, weight=10)

root.rowconfigure(0, weight=10)
root.rowconfigure(1, weight=20)
root.rowconfigure(2, weight=10)
root.rowconfigure(3, weight=10)
root.rowconfigure(4, weight=10)

Button_FoldIN = Button(root, height=2, width = 30, text="Import Folder", command=lambda: sel_folderIN())
Button_FoldIN.grid(row = 0, column = 0, padx=10,pady = 10)
Label_FoldIN = Label(root, text="NO FOLDER SELECTED",height = 1, width = 30)
Label_FoldIN.grid(row = 1, column = 0, sticky = N, padx=10,pady = 10)

Button_FoldOUT = Button(root, height=2, width=30, text="Export Folder", command=lambda: sel_folderOUT())
Button_FoldOUT.grid(row = 0, column = 2, padx=10,pady = 10)
Label_FoldOUT = Label(root, text="NO FOLDER SELECTED",height = 1, width = 30)
Label_FoldOUT.grid(row = 1, column = 2, sticky = N, padx=10,pady = 10)

Spbx_offsetFrom = Spinbox(root, width=10,from_= -127, to = 127)
Spbx_offsetFrom.grid(row = 2, column = 0, padx=10,pady = 10)

Label_To = Label(root, text="to",height = 1, width = 10)
Label_To.grid(row = 2, column = 1)

Spbx_offsetTo = Spinbox(root, width=10,from_= -127, to = 127)
Spbx_offsetTo.grid(row = 2, column = 2, padx=10,pady = 10)

Button_Run = Button(root, height = 1, width = 20, text ="RUN", command = lambda:run())
Button_Run.grid(row = 3, column = 0, columnspan=3, rowspan=2,padx=10,pady = 10)

root.mainloop()

[rdoursenaud]

Hi,

Is this using the recently published version 1.3.0?

I'd personally copy the messages to a new track rather than mutating them but I don't think this is the reason of the problem.

I think it's mostly because you didn't initialize the target's MIDI file properties, especially the resolution: ticks_per_beat argument to the MIDIFile constructor.
Ideally you also want to initialize the type and charset.

P.S.: I have edited your message to add syntax highlighting.

[rdoursenaud]

Also you may want to keep your recursion level under control by moving some of the steps into functions ;)
Otherwise, looks like a nice tool to have in the toolbox. Thanks for sharing!

[ctrl-shift-ale]

Thanks for your prompt reply. Apologies if I might be asking about basic stuff, this is my very first python script ever.
I seem to understand that in the code above, midOut is provided of a header the moment it is initialised by MidiFile() (@line 100), and that the value of ticks_per_beat might therefore differ from the source midi file (midIn @line 99)? I have no idea how to access/write heades in mido (I read the documentation though I might have missed it perhaps?). Is there any way to work with midi file headers in mido, or am I supposed to work on a lower level (which might be tricky , given my absolute non existent competence in Python) ?
Thank you so much for your patience - appreciated.

[rdoursenaud]

No problem. Congratulations on your first script!

What you want to do is replace your midOut instantiation by this one, getting the missing parameters from your midIn object:

midOut = MidFile(ticks_per_beat=midiIn.ticks_per_beat, type=midiIn.type, charset=midiIn.charset)

Please let us know if this does what you expected.