Kdenlive beat sync

beatfinder.py

import argparse
import datetime
import librosa


def parse_delta(s):
    date = datetime.datetime.strptime(s, "%H:%M:%S")
    return datetime.timedelta(
        hours=date.hour, minutes=date.minute, seconds=date.second
    )


def main():
    parser = argparse.ArgumentParser(
        prog='Kdenlive beatfinder',
        description='Creates timeline guides matching the song beat'
    )

    parser.add_argument('input_file',
        help="Audio file to analyze for beat detection")
    parser.add_argument('--output_file', default="beats.txt",
        help="Output text file for timeline guides (default: beats.txt)")
    parser.add_argument('--bpm', type=float, default=None,
        help="Force a specific tempo in beats per minute")
    parser.add_argument('--offset', default="0:00:0",
        help="Time offset added to all timestamps (H:MM:SS)")
    parser.add_argument('--tightness', type=float, default=100,
        help="Beat rigidity; higher values enforce a steadier tempo")
    parser.add_argument('--beats-per-bar', type=int, default=None,
        help="Beats per bar; label guide as <bar>:<beat> (e.g. 2:3 for 2nd bar, 3rd beat)")
    parser.add_argument('--first-bar-offset', type=int, default=0,
        help="Number of pickup beats before bar 1 (labels as 0:y)")

    args = parser.parse_args()
    offset = parse_delta(args.offset)

    y, sr = librosa.load(args.input_file)
    onset_envelope = librosa.onset.onset_strength(y=y, sr=sr)
    tempo, beat_frames = librosa.beat.beat_track(
        onset_envelope=onset_envelope, bpm=args.bpm, tightness=args.tightness
    )
    beat_times = librosa.frames_to_time(beat_frames, sr=sr)

    print(f"{args.input_file} BPM: {tempo[0]:.2f}")
    print(f"Writing timeline guides to {args.output_file}...")

    with open(args.output_file, "wt") as f:
        for i, seconds in enumerate(beat_times):
            if args.beats_per_bar is None:
                label = str(i)
            else:
                if i < args.first_bar_offset:
                    bar = 0
                    beat_in_bar = i + 1
                else:
                    j = i - args.first_bar_offset
                    bar = int((j // args.beats_per_bar) + 1)
                    beat_in_bar = int((j % args.beats_per_bar) + 1)

                label = f"{bar}:{beat_in_bar}"

            timestamp = datetime.timedelta(seconds=seconds) + offset
            f.write(f"{timestamp} {label}\n")


if __name__ == '__main__':
    main()

This fork adds support for labelling bars in guides.

The --beat-per-bar specify the number of beat in each bar (must be constant). When enabled, this option will label the guides as bar:beat. For example, --beat-per-bar 4 will create measures of 4 beats, in which 13:3 would label for the third beat of the thirteenth bar

The option --first-bar-offset allows skipping the first beats (labelled as 0:x) in order to align the guides with the first bar of the song. For example, --first-bar-offset 5 will mark the first 5 beats as 0:1 to 0:5, and start the first measure on beat 6 (labelled as 1:1).