soundfile.py

"""python-soundfile is an audio library based on libsndfile, CFFI and NumPy.

Sound files can be read or written directly using the functions
`read()` and `write()`.
To read a sound file in a block-wise fashion, use `blocks()`.
Alternatively, sound files can be opened as `SoundFile` objects.

For further information, see https://python-soundfile.readthedocs.io/.

"""
__version__ = "0.10.3"

import os as _os
import sys as _sys
from platform import machine as _machine
from os import SEEK_SET, SEEK_CUR, SEEK_END
from ctypes.util import find_library as _find_library
from _soundfile import ffi as _ffi

try:
    _unicode = unicode  # doesn't exist in Python 3.x
except NameError:
    _unicode = str


_str_types = {
    'title':       0x01,
    'copyright':   0x02,
    'software':    0x03,
    'artist':      0x04,
    'comment':     0x05,
    'date':        0x06,
    'album':       0x07,
    'license':     0x08,
    'tracknumber': 0x09,
    'genre':       0x10,
}

_formats = {
    'WAV':   0x010000,  # Microsoft WAV format (little endian default).
    'AIFF':  0x020000,  # Apple/SGI AIFF format (big endian).
    'AU':    0x030000,  # Sun/NeXT AU format (big endian).
    'RAW':   0x040000,  # RAW PCM data.
    'PAF':   0x050000,  # Ensoniq PARIS file format.
    'SVX':   0x060000,  # Amiga IFF / SVX8 / SV16 format.
    'NIST':  0x070000,  # Sphere NIST format.
    'VOC':   0x080000,  # VOC files.
    'IRCAM': 0x0A0000,  # Berkeley/IRCAM/CARL
    'W64':   0x0B0000,  # Sonic Foundry's 64 bit RIFF/WAV
    'MAT4':  0x0C0000,  # Matlab (tm) V4.2 / GNU Octave 2.0
    'MAT5':  0x0D0000,  # Matlab (tm) V5.0 / GNU Octave 2.1
    'PVF':   0x0E0000,  # Portable Voice Format
    'XI':    0x0F0000,  # Fasttracker 2 Extended Instrument
    'HTK':   0x100000,  # HMM Tool Kit format
    'SDS':   0x110000,  # Midi Sample Dump Standard
    'AVR':   0x120000,  # Audio Visual Research
    'WAVEX': 0x130000,  # MS WAVE with WAVEFORMATEX
    'SD2':   0x160000,  # Sound Designer 2
    'FLAC':  0x170000,  # FLAC lossless file format
    'CAF':   0x180000,  # Core Audio File format
    'WVE':   0x190000,  # Psion WVE format
    'OGG':   0x200000,  # Xiph OGG container
    'MPC2K': 0x210000,  # Akai MPC 2000 sampler
    'RF64':  0x220000,  # RF64 WAV file
}

_subtypes = {
    'PCM_S8':    0x0001,  # Signed 8 bit data
    'PCM_16':    0x0002,  # Signed 16 bit data
    'PCM_24':    0x0003,  # Signed 24 bit data
    'PCM_32':    0x0004,  # Signed 32 bit data
    'PCM_U8':    0x0005,  # Unsigned 8 bit data (WAV and RAW only)
    'FLOAT':     0x0006,  # 32 bit float data
    'DOUBLE':    0x0007,  # 64 bit float data
    'ULAW':      0x0010,  # U-Law encoded.
    'ALAW':      0x0011,  # A-Law encoded.
    'IMA_ADPCM': 0x0012,  # IMA ADPCM.
    'MS_ADPCM':  0x0013,  # Microsoft ADPCM.
    'GSM610':    0x0020,  # GSM 6.10 encoding.
    'VOX_ADPCM': 0x0021,  # OKI / Dialogix ADPCM
    'G721_32':   0x0030,  # 32kbs G721 ADPCM encoding.
    'G723_24':   0x0031,  # 24kbs G723 ADPCM encoding.
    'G723_40':   0x0032,  # 40kbs G723 ADPCM encoding.
    'DWVW_12':   0x0040,  # 12 bit Delta Width Variable Word encoding.
    'DWVW_16':   0x0041,  # 16 bit Delta Width Variable Word encoding.
    'DWVW_24':   0x0042,  # 24 bit Delta Width Variable Word encoding.
    'DWVW_N':    0x0043,  # N bit Delta Width Variable Word encoding.
    'DPCM_8':    0x0050,  # 8 bit differential PCM (XI only)
    'DPCM_16':   0x0051,  # 16 bit differential PCM (XI only)
    'VORBIS':    0x0060,  # Xiph Vorbis encoding.
    'ALAC_16':   0x0070,  # Apple Lossless Audio Codec (16 bit).
    'ALAC_20':   0x0071,  # Apple Lossless Audio Codec (20 bit).
    'ALAC_24':   0x0072,  # Apple Lossless Audio Codec (24 bit).
    'ALAC_32':   0x0073,  # Apple Lossless Audio Codec (32 bit).
}

_endians = {
    'FILE':   0x00000000,  # Default file endian-ness.
    'LITTLE': 0x10000000,  # Force little endian-ness.
    'BIG':    0x20000000,  # Force big endian-ness.
    'CPU':    0x30000000,  # Force CPU endian-ness.
}

# libsndfile doesn't specify default subtypes, these are somehow arbitrary:
_default_subtypes = {
    'WAV':   'PCM_16',
    'AIFF':  'PCM_16',
    'AU':    'PCM_16',
    # 'RAW':  # subtype must be explicit!
    'PAF':   'PCM_16',
    'SVX':   'PCM_16',
    'NIST':  'PCM_16',
    'VOC':   'PCM_16',
    'IRCAM': 'PCM_16',
    'W64':   'PCM_16',
    'MAT4':  'DOUBLE',
    'MAT5':  'DOUBLE',
    'PVF':   'PCM_16',
    'XI':    'DPCM_16',
    'HTK':   'PCM_16',
    'SDS':   'PCM_16',
    'AVR':   'PCM_16',
    'WAVEX': 'PCM_16',
    'SD2':   'PCM_16',
    'FLAC':  'PCM_16',
    'CAF':   'PCM_16',
    'WVE':   'ALAW',
    'OGG':   'VORBIS',
    'MPC2K': 'PCM_16',
    'RF64':  'PCM_16',
}

_ffi_types = {
    'float64': 'double',
    'float32': 'float',
    'int32': 'int',
    'int16': 'short'
}

try:
    _libname = _find_library('sndfile')
    if _libname is None:
        raise OSError('sndfile library not found')
    _snd = _ffi.dlopen(_libname)
except OSError:
    if _sys.platform == 'darwin':
        _libname = 'libsndfile.dylib'
    elif _sys.platform == 'win32':
        from platform import architecture as _architecture
        _libname = 'libsndfile' + _architecture()[0] + '.dll'
    else:
        raise

    # hack for packaging tools like cx_Freeze, which
    # compress all scripts into a zip file
    # which causes __file__ to be inside this zip file

    _path = _os.path.dirname(_os.path.abspath(__file__))

    while not _os.path.isdir(_path):
        _path = _os.path.abspath(_os.path.join(_path, '..'))

    # Homebrew on Apple M1 uses a `/opt/homebrew/lib` instead of
    # `/usr/local/lib`. We are making sure we pick that up.
    if _sys.platform == 'darwin' and _machine() == 'arm64':
        _hbrew_path = '/opt/homebrew/lib/' if _os.path.isdir('/opt/homebrew/lib/') \
            else '/usr/local/lib/'
        _snd = _ffi.dlopen(_os.path.join(
            _hbrew_path, _libname))
    else:
        _snd = _ffi.dlopen(_os.path.join(
            _path, '_soundfile_data', _libname))

__libsndfile_version__ = _ffi.string(_snd.sf_version_string()).decode('utf-8', 'replace')
if __libsndfile_version__.startswith('libsndfile-'):
    __libsndfile_version__ = __libsndfile_version__[len('libsndfile-'):]


def read(file, frames=-1, start=0, stop=None, dtype='float64', always_2d=False,
         fill_value=None, out=None, samplerate=None, channels=None,
         format=None, subtype=None, endian=None, closefd=True):
    """Provide audio data from a sound file as NumPy array.

    By default, the whole file is read from the beginning, but the
    position to start reading can be specified with *start* and the
    number of frames to read can be specified with *frames*.
    Alternatively, a range can be specified with *start* and *stop*.

    If there is less data left in the file than requested, the rest of
    the frames are filled with *fill_value*.
    If no *fill_value* is specified, a smaller array is returned.

    Parameters
    ----------
    file : str or int or file-like object
        The file to read from.  See `SoundFile` for details.
    frames : int, optional
        The number of frames to read. If *frames* is negative, the whole
        rest of the file is read.  Not allowed if *stop* is given.
    start : int, optional
        Where to start reading.  A negative value counts from the end.
    stop : int, optional
        The index after the last frame to be read.  A negative value
        counts from the end.  Not allowed if *frames* is given.
    dtype : {'float64', 'float32', 'int32', 'int16'}, optional
        Data type of the returned array, by default ``'float64'``.
        Floating point audio data is typically in the range from
        ``-1.0`` to ``1.0``.  Integer data is in the range from
        ``-2**15`` to ``2**15-1`` for ``'int16'`` and from ``-2**31`` to
        ``2**31-1`` for ``'int32'``.

        .. note:: Reading int values from a float file will *not*
            scale the data to [-1.0, 1.0). If the file contains
            ``np.array([42.6], dtype='float32')``, you will read
            ``np.array([43], dtype='int32')`` for ``dtype='int32'``.

    Returns
    -------
    audiodata : `numpy.ndarray` or type(out)
        A two-dimensional (frames x channels) NumPy array is returned.
        If the sound file has only one channel, a one-dimensional array
        is returned.  Use ``always_2d=True`` to return a two-dimensional
        array anyway.

        If *out* was specified, it is returned.  If *out* has more
        frames than available in the file (or if *frames* is smaller
        than the length of *out*) and no *fill_value* is given, then
        only a part of *out* is overwritten and a view containing all
        valid frames is returned.
    samplerate : int
        The sample rate of the audio file.

    Other Parameters
    ----------------
    always_2d : bool, optional
        By default, reading a mono sound file will return a
        one-dimensional array.  With ``always_2d=True``, audio data is
        always returned as a two-dimensional array, even if the audio
        file has only one channel.
    fill_value : float, optional
        If more frames are requested than available in the file, the
        rest of the output is be filled with *fill_value*.  If
        *fill_value* is not specified, a smaller array is returned.
    out : `numpy.ndarray` or subclass, optional
        If *out* is specified, the data is written into the given array
        instead of creating a new array.  In this case, the arguments
        *dtype* and *always_2d* are silently ignored!  If *frames* is
        not given, it is obtained from the length of *out*.
    samplerate, channels, format, subtype, endian, closefd
        See `SoundFile`.

    Examples
    --------
    >>> import soundfile as sf
    >>> data, samplerate = sf.read('stereo_file.wav')
    >>> data
    array([[ 0.71329652,  0.06294799],
           [-0.26450912, -0.38874483],
           ...
           [ 0.67398441, -0.11516333]])
    >>> samplerate
    44100

    """
    with SoundFile(file, 'r', samplerate, channels,
                   subtype, endian, format, closefd) as f:
        frames = f._prepare_read(start, stop, frames)
        data = f.read(frames, dtype, always_2d, fill_value, out)
    return data, f.samplerate


def write(file, data, samplerate, subtype=None, endian=None, format=None,
          closefd=True):
    """Write data to a sound file.

    .. note:: If *file* exists, it will be truncated and overwritten!

    Parameters
    ----------
    file : str or int or file-like object
        The file to write to.  See `SoundFile` for details.
    data : array_like
        The data to write.  Usually two-dimensional (frames x channels),
        but one-dimensional *data* can be used for mono files.
        Only the data types ``'float64'``, ``'float32'``, ``'int32'``
        and ``'int16'`` are supported.

        .. note:: The data type of *data* does **not** select the data
                  type of the written file. Audio data will be
                  converted to the given *subtype*. Writing int values
                  to a float file will *not* scale the values to
                  [-1.0, 1.0). If you write the value ``np.array([42],
                  dtype='int32')``, to a ``subtype='FLOAT'`` file, the
                  file will then contain ``np.array([42.],
                  dtype='float32')``.

    samplerate : int
        The sample rate of the audio data.
    subtype : str, optional
        See `default_subtype()` for the default value and
        `available_subtypes()` for all possible values.

    Other Parameters
    ----------------
    format, endian, closefd
        See `SoundFile`.

    Examples
    --------
    Write 10 frames of random data to a new file:

    >>> import numpy as np
    >>> import soundfile as sf
    >>> sf.write('stereo_file.wav', np.random.randn(10, 2), 44100, 'PCM_24')

    """
    import numpy as np
    data = np.asarray(data)
    if data.ndim == 1:
        channels = 1
    else:
        channels = data.shape[1]
    with SoundFile(file, 'w', samplerate, channels,
                   subtype, endian, format, closefd) as f:
        f.write(data)


def blocks(file, blocksize=None, overlap=0, frames=-1, start=0, stop=None,
           dtype='float64', always_2d=False, fill_value=None, out=None,
           samplerate=None, channels=None,
           format=None, subtype=None, endian=None, closefd=True):
    """Return a generator for block-wise reading.

    By default, iteration starts at the beginning and stops at the end
    of the file.  Use *start* to start at a later position and *frames*
    or *stop* to stop earlier.

    If you stop iterating over the generator before it's exhausted,
    the sound file is not closed. This is normally not a problem
    because the file is opened in read-only mode. To close the file
    properly, the generator's ``close()`` method can be called.

    Parameters
    ----------
    file : str or int or file-like object
        The file to read from.  See `SoundFile` for details.
    blocksize : int
        The number of frames to read per block.
        Either this or *out* must be given.
    overlap : int, optional
        The number of frames to rewind between each block.

    Yields
    ------
    `numpy.ndarray` or type(out)
        Blocks of audio data.
        If *out* was given, and the requested frames are not an integer
        multiple of the length of *out*, and no *fill_value* was given,
        the last block will be a smaller view into *out*.

    Other Parameters
    ----------------
    frames, start, stop
        See `read()`.
    dtype : {'float64', 'float32', 'int32', 'int16'}, optional
        See `read()`.
    always_2d, fill_value, out
        See `read()`.
    samplerate, channels, format, subtype, endian, closefd
        See `SoundFile`.

    Examples
    --------
    >>> import soundfile as sf
    >>> for block in sf.blocks('stereo_file.wav', blocksize=1024):
    >>>     pass  # do something with 'block'

    """
    with SoundFile(file, 'r', samplerate, channels,
                   subtype, endian, format, closefd) as f:
        frames = f._prepare_read(start, stop, frames)
        for block in f.blocks(blocksize, overlap, frames,
                              dtype, always_2d, fill_value, out):
            yield block


class _SoundFileInfo(object):
    """Information about a SoundFile"""

    def __init__(self, file, verbose):
        self.verbose = verbose
        with SoundFile(file) as f:
            self.name = f.name
            self.samplerate = f.samplerate
            self.channels = f.channels
            self.frames = f.frames
            self.duration = float(self.frames)/f.samplerate
            self.format = f.format
            self.subtype = f.subtype
            self.endian = f.endian
            self.format_info = f.format_info
            self.subtype_info = f.subtype_info
            self.sections = f.sections
            self.extra_info = f.extra_info

    @property
    def _duration_str(self):
        hours, rest = divmod(self.duration, 3600)
        minutes, seconds = divmod(rest, 60)
        if hours >= 1:
            duration = "{0:.0g}:{1:02.0g}:{2:05.3f} h".format(hours, minutes, seconds)
        elif minutes >= 1:
            duration = "{0:02.0g}:{1:05.3f} min".format(minutes, seconds)
        elif seconds <= 1:
            duration = "{0:d} samples".format(self.frames)
        else:
            duration = "{0:.3f} s".format(seconds)
        return duration

    def __repr__(self):
        info = "\n".join(
            ["{0.name}",
             "samplerate: {0.samplerate} Hz",
             "channels: {0.channels}",
             "duration: {0._duration_str}",
             "format: {0.format_info} [{0.format}]",
             "subtype: {0.subtype_info} [{0.subtype}]"])
        if self.verbose:
            info += "\n".join(
                ["\nendian: {0.endian}",
                 "sections: {0.sections}",
                 "frames: {0.frames}",
                 'extra_info: """',
                 '    {1}"""'])
        indented_extra_info = ("\n"+" "*4).join(self.extra_info.split("\n"))
        return info.format(self, indented_extra_info)


def info(file, verbose=False):
    """Returns an object with information about a `SoundFile`.

    Parameters
    ----------
    verbose : bool
        Whether to print additional information.
    """
    return _SoundFileInfo(file, verbose)


def available_formats():
    """Return a dictionary of available major formats.

    Examples
    --------
    >>> import soundfile as sf
    >>> sf.available_formats()
    {'FLAC': 'FLAC (FLAC Lossless Audio Codec)',
     'OGG': 'OGG (OGG Container format)',
     'WAV': 'WAV (Microsoft)',
     'AIFF': 'AIFF (Apple/SGI)',
     ...
     'WAVEX': 'WAVEX (Microsoft)',
     'RAW': 'RAW (header-less)',
     'MAT5': 'MAT5 (GNU Octave 2.1 / Matlab 5.0)'}

    """
    return dict(_available_formats_helper(_snd.SFC_GET_FORMAT_MAJOR_COUNT,
                                          _snd.SFC_GET_FORMAT_MAJOR))


def available_subtypes(format=None):
    """Return a dictionary of available subtypes.

    Parameters
    ----------
    format : str
        If given, only compatible subtypes are returned.

    Examples
    --------
    >>> import soundfile as sf
    >>> sf.available_subtypes('FLAC')
    {'PCM_24': 'Signed 24 bit PCM',
     'PCM_16': 'Signed 16 bit PCM',
     'PCM_S8': 'Signed 8 bit PCM'}

    """
    subtypes = _available_formats_helper(_snd.SFC_GET_FORMAT_SUBTYPE_COUNT,
                                         _snd.SFC_GET_FORMAT_SUBTYPE)
    return dict((subtype, name) for subtype, name in subtypes
                if format is None or check_format(format, subtype))


def check_format(format, subtype=None, endian=None):
    """Check if the combination of format/subtype/endian is valid.

    Examples
    --------
    >>> import soundfile as sf
    >>> sf.check_format('WAV', 'PCM_24')
    True
    >>> sf.check_format('FLAC', 'VORBIS')
    False

    """
    try:
        return bool(_format_int(format, subtype, endian))
    except (ValueError, TypeError):
        return False


def default_subtype(format):
    """Return the default subtype for a given format.

    Examples
    --------
    >>> import soundfile as sf
    >>> sf.default_subtype('WAV')
    'PCM_16'
    >>> sf.default_subtype('MAT5')
    'DOUBLE'

    """
    _check_format(format)
    return _default_subtypes.get(format.upper())


class SoundFile(object):
    """A sound file.

    For more documentation see the __init__() docstring (which is also
    used for the online documentation (https://python-soundfile.readthedocs.io/).

    """

    def __init__(self, file, mode='r', samplerate=None, channels=None,
                 subtype=None, endian=None, format=None, closefd=True):
        """Open a sound file.

        If a file is opened with `mode` ``'r'`` (the default) or
        ``'r+'``, no sample rate, channels or file format need to be
        given because the information is obtained from the file. An
        exception is the ``'RAW'`` data format, which always requires
        these data points.

        File formats consist of three case-insensitive strings:

        * a *major format* which is by default obtained from the
          extension of the file name (if known) and which can be
          forced with the format argument (e.g. ``format='WAVEX'``).
        * a *subtype*, e.g. ``'PCM_24'``. Most major formats have a
          default subtype which is used if no subtype is specified.
        * an *endian-ness*, which doesn't have to be specified at all in
          most cases.

        A `SoundFile` object is a *context manager*, which means
        if used in a "with" statement, `close()` is automatically
        called when reaching the end of the code block inside the "with"
        statement.

        Parameters
        ----------
        file : str or int or file-like object
            The file to open.  This can be a file name, a file
            descriptor or a Python file object (or a similar object with
            the methods ``read()``/``readinto()``, ``write()``,
            ``seek()`` and ``tell()``).
        mode : {'r', 'r+', 'w', 'w+', 'x', 'x+'}, optional
            Open mode.  Has to begin with one of these three characters:
            ``'r'`` for reading, ``'w'`` for writing (truncates *file*)
            or ``'x'`` for writing (raises an error if *file* already
            exists).  Additionally, it may contain ``'+'`` to open
            *file* for both reading and writing.
            The character ``'b'`` for *binary mode* is implied because
            all sound files have to be opened in this mode.
            If *file* is a file descriptor or a file-like object,
            ``'w'`` doesn't truncate and ``'x'`` doesn't raise an error.
        samplerate : int
            The sample rate of the file.  If `mode` contains ``'r'``,
            this is obtained from the file (except for ``'RAW'`` files).
        channels : int
            The number of channels of the file.
            If `mode` contains ``'r'``, this is obtained from the file
            (except for ``'RAW'`` files).
        subtype : str, sometimes optional
            The subtype of the sound file.  If `mode` contains ``'r'``,
            this is obtained from the file (except for ``'RAW'``
            files), if not, the default value depends on the selected
            `format` (see `default_subtype()`).
            See `available_subtypes()` for all possible subtypes for
            a given `format`.
        endian : {'FILE', 'LITTLE', 'BIG', 'CPU'}, sometimes optional
            The endian-ness of the sound file.  If `mode` contains
            ``'r'``, this is obtained from the file (except for
            ``'RAW'`` files), if not, the default value is ``'FILE'``,
            which is correct in most cases.
        format : str, sometimes optional
            The major format of the sound file.  If `mode` contains
            ``'r'``, this is obtained from the file (except for
            ``'RAW'`` files), if not, the default value is determined
            from the file extension.  See `available_formats()` for
            all possible values.
        closefd : bool, optional
            Whether to close the file descriptor on `close()`. Only
            applicable if the *file* argument is a file descriptor.

        Examples
        --------
        >>> from soundfile import SoundFile

        Open an existing file for reading:

        >>> myfile = SoundFile('existing_file.wav')
        >>> # do something with myfile
        >>> myfile.close()

        Create a new sound file for reading and writing using a with
        statement:

        >>> with SoundFile('new_file.wav', 'x+', 44100, 2) as myfile:
        >>>     # do something with myfile
        >>>     # ...
        >>>     assert not myfile.closed
        >>>     # myfile.close() is called automatically at the end
        >>> assert myfile.closed

        """
        # resolve PathLike objects (see PEP519 for details):
        # can be replaced with _os.fspath(file) for Python >= 3.6
        file = file.__fspath__() if hasattr(file, '__fspath__') else file
        self._name = file
        if mode is None:
            mode = getattr(file, 'mode', None)
        mode_int = _check_mode(mode)
        self._mode = mode
        self._info = _create_info_struct(file, mode, samplerate, channels,
                                         format, subtype, endian)
        self._file = self._open(file, mode_int, closefd)
        if set(mode).issuperset('r+') and self.seekable():
            # Move write position to 0 (like in Python file objects)
            self.seek(0)
        _snd.sf_command(self._file, _snd.SFC_SET_CLIPPING, _ffi.NULL,
                        _snd.SF_TRUE)

    name = property(lambda self: self._name)
    """The file name of the sound file."""
    mode = property(lambda self: self._mode)
    """The open mode the sound file was opened with."""
    samplerate = property(lambda self: self._info.samplerate)
    """The sample rate of the sound file."""
    frames = property(lambda self: self._info.frames)
    """The number of frames in the sound file."""
    channels = property(lambda self: self._info.channels)
    """The number of channels in the sound file."""
    format = property(
        lambda self: _format_str(self._info.format & _snd.SF_FORMAT_TYPEMASK))
    """The major format of the sound file."""
    subtype = property(
        lambda self: _format_str(self._info.format & _snd.SF_FORMAT_SUBMASK))
    """The subtype of data in the the sound file."""
    endian = property(
        lambda self: _format_str(self._info.format & _snd.SF_FORMAT_ENDMASK))
    """The endian-ness of the data in the sound file."""
    format_info = property(
        lambda self: _format_info(self._info.format &
                                  _snd.SF_FORMAT_TYPEMASK)[1])
    """A description of the major format of the sound file."""
    subtype_info = property(
        lambda self: _format_info(self._info.format &
                                  _snd.SF_FORMAT_SUBMASK)[1])
    """A description of the subtype of the sound file."""
    sections = property(lambda self: self._info.sections)
    """The number of sections of the sound file."""
    closed = property(lambda self: self._file is None)
    """Whether the sound file is closed or not."""
    _errorcode = property(lambda self: _snd.sf_error(self._file))
    """A pending sndfile error code."""

    @property
    def extra_info(self):
        """Retrieve the log string generated when opening the file."""
        info = _ffi.new("char[]", 2**14)
        _snd.sf_command(self._file, _snd.SFC_GET_LOG_INFO,
                        info, _ffi.sizeof(info))
        return _ffi.string(info).decode('utf-8', 'replace')

    # avoid confusion if something goes wrong before assigning self._file:
    _file = None

    def __repr__(self):
        return ("SoundFile({0.name!r}, mode={0.mode!r}, "
                "samplerate={0.samplerate}, channels={0.channels}, "
                "format={0.format!r}, subtype={0.subtype!r}, "
                "endian={0.endian!r})".format(self))

    def __del__(self):
        self.close()

    def __enter__(self):
        return self

    def __exit__(self, *args):
        self.close()

    def __setattr__(self, name, value):
        """Write text meta-data in the sound file through properties."""
        if name in _str_types:
            self._check_if_closed()
            err = _snd.sf_set_string(self._file, _str_types[name],
                                     value.encode())
            _error_check(err)
        else:
            object.__setattr__(self, name, value)

    def __getattr__(self, name):
        """Read text meta-data in the sound file through properties."""
        if name in _str_types:
            self._check_if_closed()
            data = _snd.sf_get_string(self._file, _str_types[name])
            return _ffi.string(data).decode('utf-8', 'replace') if data else ""
        else:
            raise AttributeError(
                "'SoundFile' object has no attribute {0!r}".format(name))

    def __len__(self):
        # Note: This is deprecated and will be removed at some point,
        # see https://github.com/bastibe/python-soundfile/issues/199
        return self._info.frames

    def __bool__(self):
        # Note: This is temporary until __len__ is removed, afterwards it
        # can (and should) be removed without change of behavior
        return True

    def __nonzero__(self):
        # Note: This is only for compatibility with Python 2 and it shall be
        # removed at the same time as __bool__().
        return self.__bool__()

    def seekable(self):
        """Return True if the file supports seeking."""
        return self._info.seekable == _snd.SF_TRUE

    def seek(self, frames, whence=SEEK_SET):
        """Set the read/write position.

        Parameters
        ----------
        frames : int
            The frame index or offset to seek.
        whence : {SEEK_SET, SEEK_CUR, SEEK_END}, optional
            By default (``whence=SEEK_SET``), *frames* are counted from
            the beginning of the file.
            ``whence=SEEK_CUR`` seeks from the current position
            (positive and negative values are allowed for *frames*).
            ``whence=SEEK_END`` seeks from the end (use negative value
            for *frames*).

        Returns
        -------
        int
            The new absolute read/write position in frames.

        Examples
        --------
        >>> from soundfile import SoundFile, SEEK_END
        >>> myfile = SoundFile('stereo_file.wav')

        Seek to the beginning of the file:

        >>> myfile.seek(0)
        0

        Seek to the end of the file:

        >>> myfile.seek(0, SEEK_END)
        44100  # this is the file length

        """
        self._check_if_closed()
        position = _snd.sf_seek(self._file, frames, whence)
        _error_check(self._errorcode)
        return position

    def tell(self):
        """Return the current read/write position."""
        return self.seek(0, SEEK_CUR)

    def read(self, frames=-1, dtype='float64', always_2d=False,
             fill_value=None, out=None):
        """Read from the file and return data as NumPy array.

        Reads the given number of frames in the given data format
        starting at the current read/write position.  This advances the
        read/write position by the same number of frames.
        By default, all frames from the current read/write position to
        the end of the file are returned.
        Use `seek()` to move the current read/write position.

        Parameters
        ----------
        frames : int, optional
            The number of frames to read. If ``frames < 0``, the whole
            rest of the file is read.
        dtype : {'float64', 'float32', 'int32', 'int16'}, optional
            Data type of the returned array, by default ``'float64'``.
            Floating point audio data is typically in the range from
            ``-1.0`` to ``1.0``. Integer data is in the range from
            ``-2**15`` to ``2**15-1`` for ``'int16'`` and from
            ``-2**31`` to ``2**31-1`` for ``'int32'``.

            .. note:: Reading int values from a float file will *not*
                scale the data to [-1.0, 1.0). If the file contains
                ``np.array([42.6], dtype='float32')``, you will read
                ``np.array([43], dtype='int32')`` for
                ``dtype='int32'``.

        Returns
        -------
        audiodata : `numpy.ndarray` or type(out)
            A two-dimensional NumPy (frames x channels) array is
            returned. If the sound file has only one channel, a
            one-dimensional array is returned. Use ``always_2d=True``
            to return a two-dimensional array anyway.

            If *out* was specified, it is returned. If *out* has more
            frames than available in the file (or if *frames* is
            smaller than the length of *out*) and no *fill_value* is
            given, then only a part of *out* is overwritten and a view
            containing all valid frames is returned.

        Other Parameters
        ----------------
        always_2d : bool, optional
            By default, reading a mono sound file will return a
            one-dimensional array. With ``always_2d=True``, audio data
            is always returned as a two-dimensional array, even if the
            audio file has only one channel.
        fill_value : float, optional
            If more frames are requested than available in the file,
            the rest of the output is be filled with *fill_value*. If
            *fill_value* is not specified, a smaller array is
            returned.
        out : `numpy.ndarray` or subclass, optional
            If *out* is specified, the data is written into the given
            array instead of creating a new array. In this case, the
            arguments *dtype* and *always_2d* are silently ignored! If
            *frames* is not given, it is obtained from the length of
            *out*.

        Examples
        --------
        >>> from soundfile import SoundFile
        >>> myfile = SoundFile('stereo_file.wav')

        Reading 3 frames from a stereo file:

        >>> myfile.read(3)
        array([[ 0.71329652,  0.06294799],
               [-0.26450912, -0.38874483],
               [ 0.67398441, -0.11516333]])
        >>> myfile.close()

        See Also
        --------
        buffer_read, .write

        """
        if out is None:
            frames = self._check_frames(frames, fill_value)
            out = self._create_empty_array(frames, always_2d, dtype)
        else:
            if frames < 0 or frames > len(out):
                frames = len(out)
        frames = self._array_io('read', out, frames)
        if len(out) > frames:
            if fill_value is None:
                out = out[:frames]
            else:
                out[frames:] = fill_value
        return out

    def buffer_read(self, frames=-1, dtype=None):
        """Read from the file and return data as buffer object.

        Reads the given number of *frames* in the given data format
        starting at the current read/write position.  This advances the
        read/write position by the same number of frames.
        By default, all frames from the current read/write position to
        the end of the file are returned.
        Use `seek()` to move the current read/write position.

        Parameters
        ----------
        frames : int, optional
            The number of frames to read. If ``frames < 0``, the whole
            rest of the file is read.
        dtype : {'float64', 'float32', 'int32', 'int16'}
            Audio data will be converted to the given data type.

        Returns
        -------
        buffer
            A buffer containing the read data.

        See Also
        --------
        buffer_read_into, .read, buffer_write

        """
        frames = self._check_frames(frames, fill_value=None)
        ctype = self._check_dtype(dtype)
        cdata = _ffi.new(ctype + '[]', frames * self.channels)
        read_frames = self._cdata_io('read', cdata, ctype, frames)
        assert read_frames == frames
        return _ffi.buffer(cdata)

    def buffer_read_into(self, buffer, dtype):
        """Read from the file into a given buffer object.

        Fills the given *buffer* with frames in the given data format
        starting at the current read/write position (which can be
        changed with `seek()`) until the buffer is full or the end
        of the file is reached.  This advances the read/write position
        by the number of frames that were read.

        Parameters
        ----------
        buffer : writable buffer
            Audio frames from the file are written to this buffer.
        dtype : {'float64', 'float32', 'int32', 'int16'}
            The data type of *buffer*.

        Returns
        -------
        int
            The number of frames that were read from the file.
            This can be less than the size of *buffer*.
            The rest of the buffer is not filled with meaningful data.

        See Also
        --------
        buffer_read, .read

        """
        ctype = self._check_dtype(dtype)
        cdata, frames = self._check_buffer(buffer, ctype)
        frames = self._cdata_io('read', cdata, ctype, frames)
        return frames

    def write(self, data):
        """Write audio data from a NumPy array to the file.

        Writes a number of frames at the read/write position to the
        file. This also advances the read/write position by the same
        number of frames and enlarges the file if necessary.

        Note that writing int values to a float file will *not* scale
        the values to [-1.0, 1.0). If you write the value
        ``np.array([42], dtype='int32')``, to a ``subtype='FLOAT'``
        file, the file will then contain ``np.array([42.],
        dtype='float32')``.

        Parameters
        ----------
        data : array_like
            The data to write. Usually two-dimensional (frames x
            channels), but one-dimensional *data* can be used for mono
            files. Only the data types ``'float64'``, ``'float32'``,
            ``'int32'`` and ``'int16'`` are supported.

            .. note:: The data type of *data* does **not** select the
                  data type of the written file. Audio data will be
                  converted to the given *subtype*. Writing int values
                  to a float file will *not* scale the values to
                  [-1.0, 1.0). If you write the value ``np.array([42],
                  dtype='int32')``, to a ``subtype='FLOAT'`` file, the
                  file will then contain ``np.array([42.],
                  dtype='float32')``.

        Examples
        --------
        >>> import numpy as np
        >>> from soundfile import SoundFile
        >>> myfile = SoundFile('stereo_file.wav')

        Write 10 frames of random data to a new file:

        >>> with SoundFile('stereo_file.wav', 'w', 44100, 2, 'PCM_24') as f:
        >>>     f.write(np.random.randn(10, 2))

        See Also
        --------
        buffer_write, .read

        """
        import numpy as np
        # no copy is made if data has already the correct memory layout:
        data = np.ascontiguousarray(data)
        written = self._array_io('write', data, len(data))
        assert written == len(data)
        self._update_frames(written)

    def buffer_write(self, data, dtype):
        """Write audio data from a buffer/bytes object to the file.

        Writes the contents of *data* to the file at the current
        read/write position.
        This also advances the read/write position by the number of
        frames that were written and enlarges the file if necessary.

        Parameters
        ----------
        data : buffer or bytes
            A buffer or bytes object containing the audio data to be
            written.
        dtype : {'float64', 'float32', 'int32', 'int16'}
            The data type of the audio data stored in *data*.

        See Also
        --------
        .write, buffer_read

        """
        ctype = self._check_dtype(dtype)
        cdata, frames = self._check_buffer(data, ctype)
        written = self._cdata_io('write', cdata, ctype, frames)
        assert written == frames
        self._update_frames(written)

    def blocks(self, blocksize=None, overlap=0, frames=-1, dtype='float64',
               always_2d=False, fill_value=None, out=None):
        """Return a generator for block-wise reading.

        By default, the generator yields blocks of the given
        *blocksize* (using a given *overlap*) until the end of the file
        is reached; *frames* can be used to stop earlier.

        Parameters
        ----------
        blocksize : int
            The number of frames to read per block. Either this or *out*
            must be given.
        overlap : int, optional
            The number of frames to rewind between each block.
        frames : int, optional
            The number of frames to read.
            If ``frames < 0``, the file is read until the end.
        dtype : {'float64', 'float32', 'int32', 'int16'}, optional
            See `read()`.

        Yields
        ------
        `numpy.ndarray` or type(out)
            Blocks of audio data.
            If *out* was given, and the requested frames are not an
            integer multiple of the length of *out*, and no
            *fill_value* was given, the last block will be a smaller
            view into *out*.


        Other Parameters
        ----------------
        always_2d, fill_value, out
            See `read()`.
        fill_value : float, optional
            See `read()`.
        out : `numpy.ndarray` or subclass, optional
            If *out* is specified, the data is written into the given
            array instead of creating a new array. In this case, the
            arguments *dtype* and *always_2d* are silently ignored!

        Examples
        --------
        >>> from soundfile import SoundFile
        >>> with SoundFile('stereo_file.wav') as f:
        >>>     for block in f.blocks(blocksize=1024):
        >>>         pass  # do something with 'block'

        """
        import numpy as np

        if 'r' not in self.mode and '+' not in self.mode:
            raise SoundFileRuntimeError("blocks() is not allowed in write-only mode")

        if out is None:
            if blocksize is None:
                raise TypeError("One of {blocksize, out} must be specified")
            out = self._create_empty_array(blocksize, always_2d, dtype)
            copy_out = True
        else:
            if blocksize is not None:
                raise TypeError(
                    "Only one of {blocksize, out} may be specified")
            blocksize = len(out)
            copy_out = False

        overlap_memory = None
        frames = self._check_frames(frames, fill_value)
        while frames > 0:
            if overlap_memory is None:
                output_offset = 0
            else:
                output_offset = len(overlap_memory)
                out[:output_offset] = overlap_memory

            toread = min(blocksize - output_offset, frames)
            self.read(toread, dtype, always_2d, fill_value, out[output_offset:])

            if overlap:
                if overlap_memory is None:
                    overlap_memory = np.copy(out[-overlap:])
                else:
                    overlap_memory[:] = out[-overlap:]

            if blocksize > frames + overlap and fill_value is None:
                block = out[:frames + overlap]
            else:
                block = out
            yield np.copy(block) if copy_out else block
            frames -= toread

    def truncate(self, frames=None):
        """Truncate the file to a given number of frames.

        After this command, the read/write position will be at the new
        end of the file.

        Parameters
        ----------
        frames : int, optional
            Only the data before *frames* is kept, the rest is deleted.
            If not specified, the current read/write position is used.

        """
        if frames is None:
            frames = self.tell()
        err = _snd.sf_command(self._file, _snd.SFC_FILE_TRUNCATE,
                              _ffi.new("sf_count_t*", frames),
                              _ffi.sizeof("sf_count_t"))
        if err:
            # get the actual error code
            err = _snd.sf_error(self._file)
            raise LibsndfileError(err, "Error truncating the file")
        self._info.frames = frames

    def set_compression_level(self, level):
        """Set the compression level 

        The compression level should be between 0.0 (minimum compression 
        level) and 1.0 (highest compression level). Currenly this command 
        is only implemented for FLAC and Ogg/Vorbis files. It has no 
        effect on uncompressed file formats.

        Setting the compression level is only valid when open in 
        write mode. This method must be called before any data is actually
        written

        Parameters
        ----------
        level : float
            The compression level, between 0. (minimum compression) and
            1.0 (highest  compression)
        """
        if self._mode == 'r':
            raise SoundFileRuntimeError("Cannot set compression level "
                                        "for a file in 'read' mode")

        err = _snd.sf_command(self._file, _snd.SFC_SET_COMPRESSION_LEVEL,
                              _ffi.new("double*", level),
                              _ffi.sizeof("double"))
        if err == SF_FALSE
            err = _snd.sf_error(self._file)
            raise LibsndfileError(err, "Error setting the compression level")

    def set_vbr_encoding_quality(self, quality):
        """Set the Variable Bit Rate encoding quality.

        The encoding quality value should be between 0.0 (lowest quality) 
        and 1.0 (highest quality). Currenly this command is only implemented
        for FLAC and Ogg/Vorbis files. It has no effect on un-compressed file 
        formats. 
        
        Parameters
        ----------
        quality : float
            The encoding quality as a value between 0.0 (lowest quality) and
            1.0 (highest quality)
        """
        if self._mode == 'r':
            raise SoundFileRuntimeError("Cannot set VBR encoding quality "
                                        "for a file in 'read' mode")

        err = _snd.sf_command(self._file, _snd.SFC_SET_VBR_ENCODING_QUALITY,
                              _ffi.new("double*", quality),
                              _ffi.sizeof("double"))

        if err == SF_FALSE
            err = _snd.sf_error(self._file)
            raise LibsndfileError(err, "Error setting the encoding quality")
            

    def flush(self):
        """Write unwritten data to the file system.

        Data written with `write()` is not immediately written to
        the file system but buffered in memory to be written at a later
        time.  Calling `flush()` makes sure that all changes are
        actually written to the file system.

        This has no effect on files opened in read-only mode.

        """
        self._check_if_closed()
        _snd.sf_write_sync(self._file)

    def close(self):
        """Close the file.  Can be called multiple times."""
        if not self.closed:
            # be sure to flush data to disk before closing the file
            self.flush()
            err = _snd.sf_close(self._file)
            self._file = None
            _error_check(err)

    def _open(self, file, mode_int, closefd):
        """Call the appropriate sf_open*() function from libsndfile."""
        if isinstance(file, (_unicode, bytes)):
            if _os.path.isfile(file):
                if 'x' in self.mode:
                    raise OSError("File exists: {0!r}".format(self.name))
                elif set(self.mode).issuperset('w+'):
                    # truncate the file, because SFM_RDWR doesn't:
                    _os.close(_os.open(file, _os.O_WRONLY | _os.O_TRUNC))
            openfunction = _snd.sf_open
            if isinstance(file, _unicode):
                if _sys.platform == 'win32':
                    openfunction = _snd.sf_wchar_open
                else:
                    file = file.encode(_sys.getfilesystemencoding())
            file_ptr = openfunction(file, mode_int, self._info)
        elif isinstance(file, int):
            file_ptr = _snd.sf_open_fd(file, mode_int, self._info, closefd)
        elif _has_virtual_io_attrs(file, mode_int):
            file_ptr = _snd.sf_open_virtual(self._init_virtual_io(file),
                                            mode_int, self._info, _ffi.NULL)
        else:
            raise TypeError("Invalid file: {0!r}".format(self.name))
        if file_ptr == _ffi.NULL:
            # get the actual error code
            err = _snd.sf_error(file_ptr)
            raise LibsndfileError(err, prefix="Error opening {0!r}: ".format(self.name))
        if mode_int == _snd.SFM_WRITE:
            # Due to a bug in libsndfile version <= 1.0.25, frames != 0
            # when opening a named pipe in SFM_WRITE mode.
            # See http://github.com/erikd/libsndfile/issues/77.
            self._info.frames = 0
            # This is not necessary for "normal" files (because
            # frames == 0 in this case), but it doesn't hurt, either.
        return file_ptr

    def _init_virtual_io(self, file):
        """Initialize callback functions for sf_open_virtual()."""
        @_ffi.callback("sf_vio_get_filelen")
        def vio_get_filelen(user_data):
            curr = file.tell()
            file.seek(0, SEEK_END)
            size = file.tell()
            file.seek(curr, SEEK_SET)
            return size

        @_ffi.callback("sf_vio_seek")
        def vio_seek(offset, whence, user_data):
            file.seek(offset, whence)
            return file.tell()

        @_ffi.callback("sf_vio_read")
        def vio_read(ptr, count, user_data):
            # first try readinto(), if not available fall back to read()
            try:
                buf = _ffi.buffer(ptr, count)
                data_read = file.readinto(buf)
            except AttributeError:
                data = file.read(count)
                data_read = len(data)
                buf = _ffi.buffer(ptr, data_read)
                buf[0:data_read] = data
            return data_read

        @_ffi.callback("sf_vio_write")
        def vio_write(ptr, count, user_data):
            buf = _ffi.buffer(ptr, count)
            data = buf[:]
            written = file.write(data)
            # write() returns None for file objects in Python <= 2.7:
            if written is None:
                written = count
            return written

        @_ffi.callback("sf_vio_tell")
        def vio_tell(user_data):
            return file.tell()

        # Note: the callback functions must be kept alive!
        self._virtual_io = {'get_filelen': vio_get_filelen,
                            'seek': vio_seek,
                            'read': vio_read,
                            'write': vio_write,
                            'tell': vio_tell}

        return _ffi.new("SF_VIRTUAL_IO*", self._virtual_io)

    def _getAttributeNames(self):
        """Return all attributes used in __setattr__ and __getattr__.

        This is useful for auto-completion (e.g. IPython).

        """
        return _str_types

    def _check_if_closed(self):
        """Check if the file is closed and raise an error if it is.

        This should be used in every method that uses self._file.

        """
        if self.closed:
            raise SoundFileRuntimeError("I/O operation on closed file")

    def _check_frames(self, frames, fill_value):
        """Reduce frames to no more than are available in the file."""
        if self.seekable():
            remaining_frames = self.frames - self.tell()
            if frames < 0 or (frames > remaining_frames and
                              fill_value is None):
                frames = remaining_frames
        elif frames < 0:
            raise ValueError("frames must be specified for non-seekable files")
        return frames

    def _check_buffer(self, data, ctype):
        """Convert buffer to cdata and check for valid size."""
        assert ctype in _ffi_types.values()
        if not isinstance(data, bytes):
            data = _ffi.from_buffer(data)
        frames, remainder = divmod(len(data),
                                   self.channels * _ffi.sizeof(ctype))
        if remainder:
            raise ValueError("Data size must be a multiple of frame size")
        return data, frames

    def _create_empty_array(self, frames, always_2d, dtype):
        """Create an empty array with appropriate shape."""
        import numpy as np
        if always_2d or self.channels > 1:
            shape = frames, self.channels
        else:
            shape = frames,
        return np.empty(shape, dtype, order='C')

    def _check_dtype(self, dtype):
        """Check if dtype string is valid and return ctype string."""
        try:
            return _ffi_types[dtype]
        except KeyError:
            raise ValueError("dtype must be one of {0!r} and not {1!r}".format(
                sorted(_ffi_types.keys()), dtype))

    def _array_io(self, action, array, frames):
        """Check array and call low-level IO function."""
        if (array.ndim not in (1, 2) or
                array.ndim == 1 and self.channels != 1 or
                array.ndim == 2 and array.shape[1] != self.channels):
            raise ValueError("Invalid shape: {0!r}".format(array.shape))
        if not array.flags.c_contiguous:
            raise ValueError("Data must be C-contiguous")
        ctype = self._check_dtype(array.dtype.name)
        assert array.dtype.itemsize == _ffi.sizeof(ctype)
        cdata = _ffi.cast(ctype + '*', array.__array_interface__['data'][0])
        return self._cdata_io(action, cdata, ctype, frames)

    def _cdata_io(self, action, data, ctype, frames):
        """Call one of libsndfile's read/write functions."""
        assert ctype in _ffi_types.values()
        self._check_if_closed()
        if self.seekable():
            curr = self.tell()
        func = getattr(_snd, 'sf_' + action + 'f_' + ctype)
        frames = func(self._file, data, frames)
        _error_check(self._errorcode)
        if self.seekable():
            self.seek(curr + frames, SEEK_SET)  # Update read & write position
        return frames

    def _update_frames(self, written):
        """Update self.frames after writing."""
        if self.seekable():
            curr = self.tell()
            self._info.frames = self.seek(0, SEEK_END)
            self.seek(curr, SEEK_SET)
        else:
            self._info.frames += written

    def _prepare_read(self, start, stop, frames):
        """Seek to start frame and calculate length."""
        if start != 0 and not self.seekable():
            raise ValueError("start is only allowed for seekable files")
        if frames >= 0 and stop is not None:
            raise TypeError("Only one of {frames, stop} may be used")

        start, stop, _ = slice(start, stop).indices(self.frames)
        if stop < start:
            stop = start
        if frames < 0:
            frames = stop - start
        if self.seekable():
            self.seek(start, SEEK_SET)
        return frames

    def copy_metadata(self):
        """Get all metadata present in this SoundFile

        Returns
        -------

        metadata: dict[str, str]
            A dict with all metadata. Possible keys are: 'title', 'copyright', 
            'software', 'artist', 'comment', 'date', 'album', 'license', 
            'tracknumber' and 'genre'. 
        """
        strs = {}
        for strtype, strid in _str_types.items():
            data = _snd.sf_get_string(self._file, strid)
            if data:
                strs[strtype] = _ffi.string(data).decode('utf-8', 'replace')
        return strs



def _error_check(err, prefix=""):
    """Raise LibsndfileError if there is an error."""
    if err != 0:
        raise LibsndfileError(err, prefix=prefix)


def _format_int(format, subtype, endian):
    """Return numeric ID for given format|subtype|endian combo."""
    result = _check_format(format)
    if subtype is None:
        subtype = default_subtype(format)
        if subtype is None:
            raise TypeError(
                "No default subtype for major format {0!r}".format(format))
    elif not isinstance(subtype, (_unicode, str)):
        raise TypeError("Invalid subtype: {0!r}".format(subtype))
    try:
        result |= _subtypes[subtype.upper()]
    except KeyError:
        raise ValueError("Unknown subtype: {0!r}".format(subtype))
    if endian is None:
        endian = 'FILE'
    elif not isinstance(endian, (_unicode, str)):
        raise TypeError("Invalid endian-ness: {0!r}".format(endian))
    try:
        result |= _endians[endian.upper()]
    except KeyError:
        raise ValueError("Unknown endian-ness: {0!r}".format(endian))

    info = _ffi.new("SF_INFO*")
    info.format = result
    info.channels = 1
    if _snd.sf_format_check(info) == _snd.SF_FALSE:
        raise ValueError(
            "Invalid combination of format, subtype and endian")
    return result


def _check_mode(mode):
    """Check if mode is valid and return its integer representation."""
    if not isinstance(mode, (_unicode, str)):
        raise TypeError("Invalid mode: {0!r}".format(mode))
    mode_set = set(mode)
    if mode_set.difference('xrwb+') or len(mode) > len(mode_set):
        raise ValueError("Invalid mode: {0!r}".format(mode))
    if len(mode_set.intersection('xrw')) != 1:
        raise ValueError("mode must contain exactly one of 'xrw'")

    if '+' in mode_set:
        mode_int = _snd.SFM_RDWR
    elif 'r' in mode_set:
        mode_int = _snd.SFM_READ
    else:
        mode_int = _snd.SFM_WRITE
    return mode_int


def _create_info_struct(file, mode, samplerate, channels,
                        format, subtype, endian):
    """Check arguments and create SF_INFO struct."""
    original_format = format
    if format is None:
        format = _get_format_from_filename(file, mode)
        assert isinstance(format, (_unicode, str))
    else:
        _check_format(format)

    info = _ffi.new("SF_INFO*")
    if 'r' not in mode or format.upper() == 'RAW':
        if samplerate is None:
            raise TypeError("samplerate must be specified")
        info.samplerate = samplerate
        if channels is None:
            raise TypeError("channels must be specified")
        info.channels = channels
        info.format = _format_int(format, subtype, endian)
    else:
        if any(arg is not None for arg in (
                samplerate, channels, original_format, subtype, endian)):
            raise TypeError("Not allowed for existing files (except 'RAW'): "
                            "samplerate, channels, format, subtype, endian")
    return info


def _get_format_from_filename(file, mode):
    """Return a format string obtained from file (or file.name).

    If file already exists (= read mode), an empty string is returned on
    error.  If not, an exception is raised.
    The return type will always be str or unicode (even if
    file/file.name is a bytes object).

    """
    format = ''
    file = getattr(file, 'name', file)
    try:
        # This raises an exception if file is not a (Unicode/byte) string:
        format = _os.path.splitext(file)[-1][1:]
        # Convert bytes to unicode (raises AttributeError on Python 3 str):
        format = format.decode('utf-8', 'replace')
    except Exception:
        pass
    if format.upper() not in _formats and 'r' not in mode:
        raise TypeError("No format specified and unable to get format from "
                        "file extension: {0!r}".format(file))
    return format


def _format_str(format_int):
    """Return the string representation of a given numeric format."""
    for dictionary in _formats, _subtypes, _endians:
        for k, v in dictionary.items():
            if v == format_int:
                return k
    else:
        return 'n/a'


def _format_info(format_int, format_flag=_snd.SFC_GET_FORMAT_INFO):
    """Return the ID and short description of a given format."""
    format_info = _ffi.new("SF_FORMAT_INFO*")
    format_info.format = format_int
    _snd.sf_command(_ffi.NULL, format_flag, format_info,
                    _ffi.sizeof("SF_FORMAT_INFO"))
    name = format_info.name
    return (_format_str(format_info.format),
            _ffi.string(name).decode('utf-8', 'replace') if name else "")


def _available_formats_helper(count_flag, format_flag):
    """Helper for available_formats() and available_subtypes()."""
    count = _ffi.new("int*")
    _snd.sf_command(_ffi.NULL, count_flag, count, _ffi.sizeof("int"))
    for format_int in range(count[0]):
        yield _format_info(format_int, format_flag)


def _check_format(format_str):
    """Check if `format_str` is valid and return format ID."""
    if not isinstance(format_str, (_unicode, str)):
        raise TypeError("Invalid format: {0!r}".format(format_str))
    try:
        format_int = _formats[format_str.upper()]
    except KeyError:
        raise ValueError("Unknown format: {0!r}".format(format_str))
    return format_int


def _has_virtual_io_attrs(file, mode_int):
    """Check if file has all the necessary attributes for virtual IO."""
    readonly = mode_int == _snd.SFM_READ
    writeonly = mode_int == _snd.SFM_WRITE
    return all([
        hasattr(file, 'seek'),
        hasattr(file, 'tell'),
        hasattr(file, 'write') or readonly,
        hasattr(file, 'read') or hasattr(file, 'readinto') or writeonly,
    ])


class SoundFileError(Exception):
    """Base class for all soundfile-specific errors."""
    pass

class SoundFileRuntimeError(SoundFileError, RuntimeError):
    """soundfile module runtime error.

    Errors that used to be `RuntimeError`."""
    pass

class LibsndfileError(SoundFileRuntimeError):
    """libsndfile errors.


    Attributes
    ----------
    code
        libsndfile internal error number.
    """
    def __init__(self, code, prefix=""):
        SoundFileRuntimeError.__init__(self, code, prefix)
        self.code = code
        self.prefix = prefix

    @property
    def error_string(self):
        """Raw libsndfile error message."""
        if self.code:
            err_str = _snd.sf_error_number(self.code)
            return _ffi.string(err_str).decode('utf-8', 'replace')
        else:
            # Due to race conditions, if used concurrently, sf_error() may
            # return 0 (= no error) even if an error has happened.
            # See https://github.com/erikd/libsndfile/issues/610 for details.
            return "(Garbled error message from libsndfile)"

    def __str__(self):
        return self.prefix + self.error_string