soundfile
An audio library based on libsndfile, CFFI and NumPy
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Description
python-soundfile
================
|version| |python| |status| |license|
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The `soundfile <https://github.com/bastibe/python-soundfile>`__ module is an audio
library based on libsndfile, CFFI and NumPy. Full documentation is
available on https://python-soundfile.readthedocs.io/.
The ``soundfile`` module can read and write sound files. File reading/writing is
supported through `libsndfile <http://www.mega-nerd.com/libsndfile/>`__,
which is a free, cross-platform, open-source (LGPL) library for reading
and writing many different sampled sound file formats that runs on many
platforms including Windows, OS X, and Unix. It is accessed through
`CFFI <https://cffi.readthedocs.io/>`__, which is a foreign function
interface for Python calling C code. CFFI is supported for CPython 2.6+,
3.x and PyPy 2.0+. The ``soundfile`` module represents audio data as NumPy arrays.
| python-soundfile is BSD licensed (BSD 3-Clause License).
| (c) 2013, Bastian Bechtold
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Breaking Changes
----------------
The ``soundfile`` module has evolved rapidly in the past. Most
notably, we changed the import name from ``import pysoundfile`` to
``import soundfile`` in 0.7. In 0.6, we cleaned up many small
inconsistencies, particularly in the the ordering and naming of
function arguments and the removal of the indexing interface.
In 0.8.0, we changed the default value of ``always_2d`` from ``True``
to ``False``. Also, the order of arguments of the ``write`` function
changed from ``write(data, file, ...)`` to ``write(file, data, ...)``.
In 0.9.0, we changed the ``ctype`` arguments of the ``buffer_*``
methods to ``dtype``, using the Numpy ``dtype`` notation. The old
``ctype`` arguments still work, but are now officially deprecated.
In 0.12.0, we changed the load order of the libsndfile library. Now,
the packaged libsndfile in the platform-specific wheels is tried
before falling back to any system-provided libsndfile. If you would
prefer using the system-provided libsndfile, install the source
package or source wheel instead of the platform-specific wheels.
Installation
------------
The ``soundfile`` module depends on the Python packages CFFI and NumPy, and the
library libsndfile.
In a modern Python, you can use ``pip install soundfile`` to download
and install the latest release of the ``soundfile`` module and its
dependencies. On Windows (64/32) and OS X (Intel/ARM) and Linux 64,
this will also install a current version of the library libsndfile. If
you install the source module, you need to install libsndfile using
your distribution's package manager, for example ``sudo apt install
libsndfile1``.
If you are running on an unusual platform or if you are using an older
version of Python, you might need to install NumPy and CFFI separately,
for example using the Anaconda_ package manager.
.. _Anaconda: https://www.continuum.io/downloads
Building
--------
``Soundfile`` itself does not contain any compiled code and can be
bundled into a wheel with the usual ``python setup.py bdist_wheel``.
However, ``soundfile`` relies on libsndfile, and optionally ships its
own copy of libsndfile in the wheel.
To build a binary wheel that contains libsndfile, make sure to
checkout and update the ``_soundfile_data`` submodule, then run
``python setup.py bdist_wheel`` as usual. If the resulting file size
of the wheel is around one megabyte, a matching libsndfile has been
bundled (without libsndfile, it's around 25 KB).
To build binary wheels for all supported platforms, run ``python
build_wheels.py``, which will ``python setup.py bdist_wheel`` for each
of the platforms we have precompiled libsndfiles for.
Error Reporting
---------------
In case of API usage errors the ``soundfile`` module raises the usual `ValueError` or `TypeError`.
For other errors `SoundFileError` is raised (used to be `RuntimeError`).
Particularly, a `LibsndfileError` subclass of this exception is raised on
errors reported by the libsndfile library. In that case the exception object
provides the libsndfile internal error code in the `LibsndfileError.code` attribute and the raw
libsndfile error message in the `LibsndfileError.error_string` attribute.
Read/Write Functions
--------------------
Data can be written to the file using `soundfile.write()`, or read from
the file using `soundfile.read()`. The ``soundfile`` module can open all file formats
that `libsndfile supports
<http://www.mega-nerd.com/libsndfile/#Features>`__, for example WAV,
FLAC, OGG and MAT files (see `Known Issues <https://github.com/bastibe/python-soundfile#known-issues>`__ below about writing OGG files).
Here is an example for a program that reads a wave file and copies it
into an FLAC file:
.. code:: python
import soundfile as sf
data, samplerate = sf.read('existing_file.wav')
sf.write('new_file.flac', data, samplerate)
Block Processing
----------------
Sound files can also be read in short, optionally overlapping blocks
with `soundfile.blocks()`.
For example, this calculates the signal level for each block of a long
file:
.. code:: python
import numpy as np
import soundfile as sf
rms = [np.sqrt(np.mean(block**2)) for block in
sf.blocks('myfile.wav', blocksize=1024, overlap=512)]
``SoundFile`` Objects
---------------------
Sound files can also be opened as `SoundFile` objects. Every
`SoundFile` has a specific sample rate, data format and a set number of
channels.
If a file is opened, it is kept open for as long as the `SoundFile`
object exists. The file closes when the object is garbage collected,
but you should use the `SoundFile.close()` method or the
context manager to close the file explicitly:
.. code:: python
import soundfile as sf
with sf.SoundFile('myfile.wav', 'r+') as f:
while f.tell() < f.frames:
pos = f.tell()
data = f.read(1024)
f.seek(pos)
f.write(data*2)
All data access uses frames as index. A frame is one discrete time-step
in the sound file. Every frame contains as many samples as there are
channels in the file.
RAW Files
---------
`soundfile.read()` can usually auto-detect the file type of sound files. This
is not possible for RAW files, though:
.. code:: python
import soundfile as sf
data, samplerate = sf.read('myfile.raw', channels=1, samplerate=44100,
subtype='FLOAT')
Note that on x86, this defaults to ``endian='LITTLE'``. If you are
reading big endian data (mostly old PowerPC/6800-based files), you
have to set ``endian='BIG'`` accordingly.
You can write RAW files in a similar way, but be advised that in most
cases, a more expressive format is better and should be used instead.
Virtual IO
----------
If you have an open file-like object, `soundfile.read()` can open it just like
regular files:
.. code:: python
import soundfile as sf
with open('filename.flac', 'rb') as f:
data, samplerate = sf.read(f)
Here is an example using an HTTP request:
.. code:: python
import io
import soundfile as sf
from urllib.request import urlopen
url = "http://tinyurl.com/shepard-risset"
data, samplerate = sf.read(io.BytesIO(urlopen(url).read()))
Note that the above example only works with Python 3.x.
For Python 2.x support, replace the third line with:
.. code:: python
from urllib2 import urlopen
In-memory files
^^^^^^^^^^^^^^^
Chunks of audio, i.e. `bytes`, can also be read and written without touching the filesystem.
In the following example OGG is converted to WAV entirely in memory (without writing files to the disk):
.. code:: python
import io
import soundfile as sf
def ogg2wav(ogg: bytes):
ogg_buf = io.BytesIO(ogg)
ogg_buf.name = 'file.ogg'
data, samplerate = sf.read(ogg_buf)
wav_buf = io.BytesIO()
wav_buf.name = 'file.wav'
sf.write(wav_buf, data, samplerate)
wav_buf.seek(0) # Necessary for `.read()` to return all bytes
return wav_buf.read()
Controlling bitrate mode and compression level
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
For some audio formats, you can control the bitrate and compression level.
`compression_level` is a float between 0 and 1, with 1 being the highest compression,
and `bitrate_mode` is 'VARIABLE', 'CONSTANT', or 'AVERAGE'.
.. code:: python
import soundfile as sf
# for example, this uncompressed 5 minute wav file with 32 kHz sample rate is 18 Mb
data, samplerate = sf.read('5min_32kHz.wav')
# maximum mp3 compression results in 1.1 Mb file, with either CONSTANT or VARIABLE bit rate
sf.write('max_compression_vbr.mp3', data, samplerate, bitrate_mode='VARIABLE', compression_level=.99)
sf.write('max_compression_cbr.mp3', data, samplerate, bitrate_mode='CONSTANT', compression_level=.99)
# minimum mp3 compression results in 3.5 Mb file
sf.write('min_compression_vbr.mp3', data, samplerate, bitrate_mode='VARIABLE', compression_level=0)
Known Issues
------------
Writing to OGG files can result in empty files with certain versions of libsndfile. See `#13