beat-machine

The Beat Machine is a library for playing with beats of songs, inspired by the creations over on /r/BeatEdits. It works both as a library and as a command-line utility that reads effects from a JSON array.

Installation

One of the Beat Machine's dependencies, madmom, requires Cython to be present before installation. If you encounter an error along the lines of:

Command "python setup.py egg_info" failed with error code 1 in /tmp/tmp1d2dis8pbuild/madmom/

Try installing Cython (pip install Cython) beforehand as a separate build step.

Examples

A few examples of common edits are available below. In all cases, multiple effects can be supplied. When more than one effect is present, effects are applied in order of appearance.

Using the CLI

The CLI has the following usage (produced by python -m beatmachine --help):

Usage: __main__.py [OPTIONS]

Options:
  --input TEXT    File to process.  [required]
  --effects TEXT  JSON representation of effects to apply.  [required]
  --output TEXT   Output mp3 file path.  [required]
  --help          Show this message and exit.

Note that the program may appear to hang due to the time taken to locate beats.

Removing every other beat

The remove effect can't have a period of 1, because that would be silly (and result in nothing to work with).

$ python -m beatmachine \
    --input "in.mp3" \
    --output "out.mp3" \
    --effects '[{"type": "remove", "period": 2}]'

Cutting every beat in half

$ python -m beatmachine \
    --input "in.mp3" \
    --output "out.mp3" \
    --effects '[{"type": "cut", "period": 1}]'

Swapping beats 2 and 4

In the swap effect, the x_period and y_period fields are interchangeable, however they can't be equal.

$ python -m beatmachine \
    --input "in.mp3" \
    --output "out.mp3" \
    --effects '[{"type": "swap", "x_period": 2, "y_period": 4}]'

Halving every beat then duplicating every other beat

$ python -m beatmachine \
    --input "in.mp3" \
    --output "out.mp3" \
    --effects '[{"type": "cut", "period": 1},
                {"type": "repeat", "period": 2, "times": 2}]'

Using the Python module

Note that load_beats_by_signal is a rather long, blocking operation (~50 seconds for a 2 minute song on a Ryzen 5 2600 w/ 16GB of RAM). Your mileage may vary.

If slightly inaccurate results are acceptable, load_beats_by_bpm is also available, which is much less CPU- and memory-intensive. This method of loading beats is not capable of handling any kind of tempo change.

Removing every other beat

import beatmachine as bm

beats = bm.loader.load_beats_by_signal('in.mp3')  # A file-like object is also acceptable
effects = [bm.effects.periodic.RemoveEveryNth(period=2)]
result = sum(bm.editor.apply_effects(beats, effects))
result.export('out.mp3')

Other results come from modifying the effects list. See the effects module and its submodules for more possibilities.

Implementing a custom effect

There are two ways to create a basic effect class:

• Create a class with the metaclass beatmachine.effects.base.EffectRegistry
• Inherit from beatmachine.effects.base.BaseEffect with metaclass beatmachine.effects.base.EffectABCMeta
  • This is recommended since it provides all the necessary attributes as an abstract base class

The resulting effect class will automatically be loadable through beatmachine.effects.load_from_dict. Make sure that any configurable parameters are specified as keyword arguments, since load_from_dict passes fields directly to __init__.