python-wavefile

Pythonic libsndfile wrapper to read and write audio files.

Features

• Writer and reader objects are context managers
• Format, channels, length, sample rate... are accessed as properties as well as text strings
• Real multichannel (not just mono/stereo)
• All libsndfile formats supported, floating point encodings by default
• Numpy based interface
• Generators for block by block reading
• Reading reuses the same data block to avoid many data allocations
• Shortened constant names for formats (Using scopes instead of prefixes)
• Matlab-like whole-file interface (not recommended in production code but quite convenient for quick scripting)
• Transparent UTF-8 handling for filenames and text strings
• No module compilation required (wraps the dll using ctypes)
• Compatible with Python >= 2.6 including Python3

You can find the latest version at: https://github.com/vokimon/python-wavefile

Wish list

• Smart format chooser
  • Use file name extension to deduce main format, if not specified
  • Use main format to deduce subformat, if not specified
• Format enumeration
  • Separate Formats scope into Formats, Subformats and Endianess
  • Expose descriptive strings for formats at the API
• Exposing sndfile command API

Installation

Binary dependencies

Python dependencies are managed by the setup.py script. But still there are a couple of C/C++ dependencies. In Debian/Ubuntu, you can install them by casting:

sudo apt-get install -y libsndfile1 portaudio19-dev

PortAudio and its Python wrapper, PyAudio, are just required in order to run the examples.

Using PyPi

pypi-install wavefile

From sources

A setup.py script is provided so the common procedure for installing python packages in you platfrom will work. For example in Debian/Ubuntu systems:

sudo python setup.py install

And for per-user installation:

python setup.py install --home=~/local

provided that you have PTYHON_PATH set properly.

Copying the wavefile directory to your project is also ok.

Examples

Writting example

from wavefile import WaveWriter, Format
import numpy as np

BUFFERSIZE = 512
NCHANNELS = 2
TITLE = "Some Noise"
ARTIST = "The Artists"

with WaveWriter('synth.ogg',
		channels=NCHANNELS,
		format=Format.OGG|Format.VORBIS,
		) as w :
	w.metadata.title = "Some Noise"
	w.metadata.artist = "The Artists"
	data = np.zeros((NCHANNELS,BUFFERSIZE), np.float32)
	for x in range(256) :
		# First channel: Saw wave sweep
		data[0,:] = (x*np.arange(BUFFERSIZE, dtype=np.float32)%BUFFERSIZE/BUFFERSIZE)
		# Second channel: Modulated square wave
		data[1,BUFFERSIZE-x*2:] =  1
		data[1,:BUFFERSIZE-x*2] = -1

		# Write it down
		w.write(data)

Playback example (using pyaudio)

import pyaudio, sys
from wavefile import WaveReader

p = pyaudio.PyAudio()
with WaveReader(sys.argv[1]) as r :

	# Print info
	print "Title:", r.metadata.title
	print "Artist:", r.metadata.artist
	print "Channels:", r.channels
	print "Format: 0x%x"%r.format
	print "Sample Rate:", r.samplerate

	# open pyaudio stream
	stream = p.open(
			format = pyaudio.paFloat32,
			channels = r.channels,
			rate = r.samplerate,
			frames_per_buffer = 512,
			output = True)

	# iterator interface (reuses one array)
	# beware of the frame size, not always 512, but 512 at least
	for frame in r.read_iter(size=512) :
		stream.write(frame.flatten(), frame.shape[1])
		sys.stdout.write("."); sys.stdout.flush()

	stream.close()

Processing example

import sys
from wavefile import WaveReader, WaveWriter

with WaveReader(sys.argv[1]) as r :
	with WaveWriter(
			'output.wav',
			channels=r.channels,
			samplerate=r.samplerate,
			) as w :
		w.metadata.title = r.metadata.title + " II"
		w.metadata.artist = r.metadata.artist

		for data in r.read_iter(size=512) :
			sys.stdout.write("."); sys.stdout.flush()
			w.write(.8*data)

While read_iter is simpler and recommended, you can still use the read function, which is closer to the C one.

import sys, numpy as np
from wavefile import WaveReader, WaveWriter

with WaveReader(sys.argv[1]) as r :
	with WaveWriter(
			'output.wav',
			channels=r.channels,
			samplerate=r.samplerate,
			) as w :
		w.metadata.title = r.metadata.title + " II"
		w.metadata.artist = r.metadata.artist

		data = np.zeros((r.channels,512), np.float32, order='F')
		nframes = r.read(data)
		while nframes :
			sys.stdout.write("."); sys.stdout.flush()
			w.write(.8*data[:,:nframes])
			nframes = r.read(data)

Notice that with read you have to reallocate the data yourself, the loop structure is somewhat more complex, and you have to slice to the actual nframes because the last block usually does not have the size you asked for. read_iter simplifies the code by transparently allocating the data block for you, reusing it for each block and slicing it when the last incomplete block arrives.

Existing alternatives (what i like and dislike)

This is 'yet another' wrapper for sndfile. A lot of them appeared just because the standard 'wave' module is quite limited on what and how it does. But none of the wrappers I found around fully suit my needs and that's because I wrote this small and incomplete one, to fit my needs. So this is a summary of what I found, just in case it is useful to anyone.

• Standard 'wave' module:

  • http://docs.python.org/library/wave.html
  • I think this is the main reason why there are many wrappers around. The standard module to do wave file loading is crap.
  • Based on sndfile but it just writes .wav files.
  • It lacks support for floating point samples, patch provided but ignored see http://bugs.python.org/issue1144504
  • unreadable getX() methods instead of properties.
  • no numpy integration
  • generators, context managers... what?
  • no whole-file shortcuts provided

• scikits.audiolab

  • git clone https://github.com/cournape/audiolab
  • Cython based + python layer
  • Dual interface: matlab like and OO
  • Property accessors to samplerate...
  • Numpy integration
  • Inplace processing
  • Not in Ubuntu
  • Within a big library

• pysndfile

  • http://savannah.nongnu.org/projects/pysndfile/
  • Swig based wrapper.
  • Direct lib library + python object wrappers
  • Unusable because it is not finished (empty read/write methods in wrapper!)

• libsndfile-python

  • http://code.google.com/p/libsndfile-python/
  • svn checkout http://libsndfile-python.googlecode.com/svn/trunk/ libsndfile-python-read-only
  • Implemented in CPython
  • numpy support
  • cpython purely wraps the library
  • wrappers build the interface
  • double layered lib and pythonic interface (not that pythonic but supports numpy)
  • Implements 'command' sndfile interface

• libsndfilectypes

  • http://code.google.com/p/pyzic/wiki/LibSndFilectypes
  • ctypes based wrapper: no compilation required
  • numpy supported
  • Windows only setup (fixable)
  • Long access to constants
  • Not inplace read (creates an array every time)

python-wavefile reuses most of the libsndfilectypes ctypes wrapper, as not requiring module compilation was seen as a good point. A pythonic layer was added on the top of it.

Version history

1.5

• MacOSX support
• Fix: Genere string accesses the proper id (closes #18)
• PyAudio an optional dependency (just used by examples)
• New stuff from libsndfile 1.0.26 included

1.4

• Works with Python 3.0 to 3.2, patch from j3ffhubb
• Works on cygwin, patch from j3ffhubb
• Added readf/writef functions, patch from Tim Langlois
• Ctypes backend clean up, removing lot of legacy code
• Using libsndfile soname (runtime packages) instead of link name (development)
• Tests can be run from setup
• Travis support

1.3

• Fix: Whole-file interface works again, regression tests added
• Added a helper script to run tests in Py2 and Py3
• Using utf8 for tags

1.2

• Seek implemented
• Removed some error handling that aborted program execution
• Removed alien reference code in 'other' folder

1.1

• Python 3 support
• Support for unicode filenames

1.0

• First version