Daily Scrum.

THE PERSONAL JOURNAL OF PETER FLORIJN

A curious mind.
A love for music.

Notes on music, technology, and the things worth sharing along the way.

Peter Florijn in Music

Garageband drummer loop to midi

Garageband contains Drummer to create automatic drummer loops. Garageband does not offer an option to export this drum loop to midi. When you want to export this drum loop to your DAW there is a workaround. A file carver that extracts a midi file from apple loop files¶ You can export the loop in AIF format. With Python script aif_to_mid you can convert this file to midi. # coding: utf-8 import argparse, os, sys parser = argparse.ArgumentParser(description="A file carver that extracts a midi file from apple loop files") parser.add_argument('-i', dest='input_file', help="path to input file to extract midi from") parser.add_argument('-d', dest='input_dir', help="path to directory of files to extract midi from") parser.add_argument('-o', dest='output_dir', default='.', help='path to output directory') parser.add_argument('-x', dest='extension', default='.aif', help='optional file extension (default .aif)') parser.add_argument('-v', dest='verbose', default=False, action='store_true', help='provide verbose output') args = parser.parse_args() # Some important file magic.. # Ref: https://github.com/colxi/midi-parser-js/wiki/MIDI-File-Format-Specifications header = b'\x4D\x54\x68\x64' footer = b'\xFF\x2F\x00' track_header = b'\x4D\x54\x72\x6B' def carve_midi(input_file, output_dir): # open the file and read it into memory try: with open(input_file, "rb") as infile: blob = infile.read() except FileNotFoundError: print("File not found: {}".format(input_file)) sys.exit(1) # first things first: find a midi header try: start_offset = blob.index(header) if args.verbose: print("Found midi header at byte offset: {}".format(start_offset)) except ValueError: print("Couldn't find a midi file header anywhere. Skipping file: {}".format(input_file)) return # ok good stuff, got a midi file, get the number of tracks ntrack_bytes = blob[start_offset+10:start_offset+12] ntrack_count = int.from_bytes(ntrack_bytes, byteorder='big') cursor = start_offset # iterate through each track and update our spot in the file for track_num in range(1, ntrack_count+1): if args.verbose: print("scanning for track {}..".format(track_num),end='') try: t_offset = blob[cursor:].index(track_header) if args.verbose: print("found track at byte offset {}..".format(cursor + t_offset)) cursor += t_offset + 4 except ValueError: print("Wierd. Found a midi header but no tracks. Do not Panic. Skipping file: ()".format(input_file)) return # find the offset for the end of the midi file via the footer bytes end_offset = cursor + blob[cursor:].index(footer) + len(footer) if args.verbose: print("No more tracks. Last byte offset: {}".format(end_offset)) # replace the original extension with .mid output_file = input_file.split("/")[-1] output_file = output_file[:-4] + ".mid" # create the output directory if one doesn't exist if not os.path.exists(output_dir): os.makedirs(output_dir) # slam your fist on the desk, curse apple for their shitty practices, then claim your prize, victorious! output_fullpath = output_dir + "/" + output_file with open(output_fullpath, "wb") as outfile: print("Processed {}. Midi file found, writing to {}".format(input_file, output_fullpath)) outfile.write(blob[start_offset:end_offset]) def main(): if args.input_file: carve_midi(args.input_file, args.output_dir) elif args.input_dir: for root, subFolders, files in os.walk(args.input_dir): for file in files: if file.endswith(args.extension): carve_midi(os.path.join(root,file), args.output_dir) else: print("Missing input file. Run with -h to get help/usage instructions.") if __name__ == "__main__": main() You can call this like in this bash script. filename=$(echo "$1" | cut -f 1 -d '.') echo "Converting loop $1 to $filename.mid" ./aif_to_mid.v1.py -v -i "/Users/peter/Library/Audio/Apple Loops/User Loops/SingleFiles/$1"

3 min read