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aifc.py31.8 KB · 948 lines
"""Stuff to parse AIFF-C and AIFF files. Unless explicitly stated otherwise, the description below is trueboth for AIFF-C files and AIFF files. An AIFF-C file has the following structure.   +-----------------+  | FORM            |  +-----------------+  | <size>          |  +----+------------+  |    | AIFC       |  |    +------------+  |    | <chunks>   |  |    |    .       |  |    |    .       |  |    |    .       |  +----+------------+ An AIFF file has the string "AIFF" instead of "AIFC". A chunk consists of an identifier (4 bytes) followed by a size (4 bytes,big endian order), followed by the data.  The size field does not includethe size of the 8 byte header. The following chunk types are recognized.   FVER      <version number of AIFF-C defining document> (AIFF-C only).  MARK      <# of markers> (2 bytes)      list of markers:          <marker ID> (2 bytes, must be > 0)          <position> (4 bytes)          <marker name> ("pstring")  COMM      <# of channels> (2 bytes)      <# of sound frames> (4 bytes)      <size of the samples> (2 bytes)      <sampling frequency> (10 bytes, IEEE 80-bit extended          floating point)      in AIFF-C files only:      <compression type> (4 bytes)      <human-readable version of compression type> ("pstring")  SSND      <offset> (4 bytes, not used by this program)      <blocksize> (4 bytes, not used by this program)      <sound data> A pstring consists of 1 byte length, a string of characters, and 0 or 1byte pad to make the total length even. Usage. Reading AIFF files:  f = aifc.open(file, 'r')where file is either the name of a file or an open file pointer.The open file pointer must have methods read(), seek(), and close().In some types of audio files, if the setpos() method is not used,the seek() method is not necessary. This returns an instance of a class with the following public methods:  getnchannels()  -- returns number of audio channels (1 for             mono, 2 for stereo)  getsampwidth()  -- returns sample width in bytes  getframerate()  -- returns sampling frequency  getnframes()    -- returns number of audio frames  getcomptype()   -- returns compression type ('NONE' for AIFF files)  getcompname()   -- returns human-readable version of             compression type ('not compressed' for AIFF files)  getparams() -- returns a namedtuple consisting of all of the             above in the above order  getmarkers()    -- get the list of marks in the audio file or None             if there are no marks  getmark(id) -- get mark with the specified id (raises an error             if the mark does not exist)  readframes(n)   -- returns at most n frames of audio  rewind()    -- rewind to the beginning of the audio stream  setpos(pos) -- seek to the specified position  tell()      -- return the current position  close()     -- close the instance (make it unusable)The position returned by tell(), the position given to setpos() andthe position of marks are all compatible and have nothing to do withthe actual position in the file.The close() method is called automatically when the class instanceis destroyed. Writing AIFF files:  f = aifc.open(file, 'w')where file is either the name of a file or an open file pointer.The open file pointer must have methods write(), tell(), seek(), andclose(). This returns an instance of a class with the following public methods:  aiff()      -- create an AIFF file (AIFF-C default)  aifc()      -- create an AIFF-C file  setnchannels(n) -- set the number of channels  setsampwidth(n) -- set the sample width  setframerate(n) -- set the frame rate  setnframes(n)   -- set the number of frames  setcomptype(type, name)          -- set the compression type and the             human-readable compression type  setparams(tuple)          -- set all parameters at once  setmark(id, pos, name)          -- add specified mark to the list of marks  tell()      -- return current position in output file (useful             in combination with setmark())  writeframesraw(data)          -- write audio frames without pathing up the             file header  writeframes(data)          -- write audio frames and patch up the file header  close()     -- patch up the file header and close the             output fileYou should set the parameters before the first writeframesraw orwriteframes.  The total number of frames does not need to be set,but when it is set to the correct value, the header does not have tobe patched up.It is best to first set all parameters, perhaps possibly thecompression type, and then write audio frames using writeframesraw.When all frames have been written, either call writeframes(b'') orclose() to patch up the sizes in the header.Marks can be added anytime.  If there are any marks, you must callclose() after all frames have been written.The close() method is called automatically when the class instanceis destroyed. When a file is opened with the extension '.aiff', an AIFF file iswritten, otherwise an AIFF-C file is written.  This default can bechanged by calling aiff() or aifc() before the first writeframes orwriteframesraw.""" import structimport builtinsimport warnings __all__ = ["Error", "open"] class Error(Exception):    pass _AIFC_version = 0xA2805140     # Version 1 of AIFF-C def _read_long(file):    try:        return struct.unpack('>l', file.read(4))[0]    except struct.error:        raise EOFError from None def _read_ulong(file):    try:        return struct.unpack('>L', file.read(4))[0]    except struct.error:        raise EOFError from None def _read_short(file):    try:        return struct.unpack('>h', file.read(2))[0]    except struct.error:        raise EOFError from None def _read_ushort(file):    try:        return struct.unpack('>H', file.read(2))[0]    except struct.error:        raise EOFError from None def _read_string(file):    length = ord(file.read(1))    if length == 0:        data = b''    else:        data = file.read(length)    if length & 1 == 0:        dummy = file.read(1)    return data _HUGE_VAL = 1.79769313486231e+308 # See <limits.h> def _read_float(f): # 10 bytes    expon = _read_short(f) # 2 bytes    sign = 1    if expon < 0:        sign = -1        expon = expon + 0x8000    himant = _read_ulong(f) # 4 bytes    lomant = _read_ulong(f) # 4 bytes    if expon == himant == lomant == 0:        f = 0.0    elif expon == 0x7FFF:        f = _HUGE_VAL    else:        expon = expon - 16383        f = (himant * 0x100000000 + lomant) * pow(2.0, expon - 63)    return sign * f def _write_short(f, x):    f.write(struct.pack('>h', x)) def _write_ushort(f, x):    f.write(struct.pack('>H', x)) def _write_long(f, x):    f.write(struct.pack('>l', x)) def _write_ulong(f, x):    f.write(struct.pack('>L', x)) def _write_string(f, s):    if len(s) > 255:        raise ValueError("string exceeds maximum pstring length")    f.write(struct.pack('B', len(s)))    f.write(s)    if len(s) & 1 == 0:        f.write(b'\x00') def _write_float(f, x):    import math    if x < 0:        sign = 0x8000        x = x * -1    else:        sign = 0    if x == 0:        expon = 0        himant = 0        lomant = 0    else:        fmant, expon = math.frexp(x)        if expon > 16384 or fmant >= 1 or fmant != fmant: # Infinity or NaN            expon = sign|0x7FFF            himant = 0            lomant = 0        else:                   # Finite            expon = expon + 16382            if expon < 0:           # denormalized                fmant = math.ldexp(fmant, expon)                expon = 0            expon = expon | sign            fmant = math.ldexp(fmant, 32)            fsmant = math.floor(fmant)            himant = int(fsmant)            fmant = math.ldexp(fmant - fsmant, 32)            fsmant = math.floor(fmant)            lomant = int(fsmant)    _write_ushort(f, expon)    _write_ulong(f, himant)    _write_ulong(f, lomant) from chunk import Chunkfrom collections import namedtuple _aifc_params = namedtuple('_aifc_params',                          'nchannels sampwidth framerate nframes comptype compname') _aifc_params.nchannels.__doc__ = 'Number of audio channels (1 for mono, 2 for stereo)'_aifc_params.sampwidth.__doc__ = 'Sample width in bytes'_aifc_params.framerate.__doc__ = 'Sampling frequency'_aifc_params.nframes.__doc__ = 'Number of audio frames'_aifc_params.comptype.__doc__ = 'Compression type ("NONE" for AIFF files)'_aifc_params.compname.__doc__ = ("""\A human-readable version of the compression type('not compressed' for AIFF files)""")  class Aifc_read:    # Variables used in this class:    #    # These variables are available to the user though appropriate    # methods of this class:    # _file -- the open file with methods read(), close(), and seek()    #       set through the __init__() method    # _nchannels -- the number of audio channels    #       available through the getnchannels() method    # _nframes -- the number of audio frames    #       available through the getnframes() method    # _sampwidth -- the number of bytes per audio sample    #       available through the getsampwidth() method    # _framerate -- the sampling frequency    #       available through the getframerate() method    # _comptype -- the AIFF-C compression type ('NONE' if AIFF)    #       available through the getcomptype() method    # _compname -- the human-readable AIFF-C compression type    #       available through the getcomptype() method    # _markers -- the marks in the audio file    #       available through the getmarkers() and getmark()    #       methods    # _soundpos -- the position in the audio stream    #       available through the tell() method, set through the    #       setpos() method    #    # These variables are used internally only:    # _version -- the AIFF-C version number    # _decomp -- the decompressor from builtin module cl    # _comm_chunk_read -- 1 iff the COMM chunk has been read    # _aifc -- 1 iff reading an AIFF-C file    # _ssnd_seek_needed -- 1 iff positioned correctly in audio    #       file for readframes()    # _ssnd_chunk -- instantiation of a chunk class for the SSND chunk    # _framesize -- size of one frame in the file     _file = None  # Set here since __del__ checks it     def initfp(self, file):        self._version = 0        self._convert = None        self._markers = []        self._soundpos = 0        self._file = file        chunk = Chunk(file)        if chunk.getname() != b'FORM':            raise Error('file does not start with FORM id')        formdata = chunk.read(4)        if formdata == b'AIFF':            self._aifc = 0        elif formdata == b'AIFC':            self._aifc = 1        else:            raise Error('not an AIFF or AIFF-C file')        self._comm_chunk_read = 0        self._ssnd_chunk = None        while 1:            self._ssnd_seek_needed = 1            try:                chunk = Chunk(self._file)            except EOFError:                break            chunkname = chunk.getname()            if chunkname == b'COMM':                self._read_comm_chunk(chunk)                self._comm_chunk_read = 1            elif chunkname == b'SSND':                self._ssnd_chunk = chunk                dummy = chunk.read(8)                self._ssnd_seek_needed = 0            elif chunkname == b'FVER':                self._version = _read_ulong(chunk)            elif chunkname == b'MARK':                self._readmark(chunk)            chunk.skip()        if not self._comm_chunk_read or not self._ssnd_chunk:            raise Error('COMM chunk and/or SSND chunk missing')     def __init__(self, f):        if isinstance(f, str):            file_object = builtins.open(f, 'rb')            try:                self.initfp(file_object)            except:                file_object.close()                raise        else:            # assume it is an open file object already            self.initfp(f)     def __enter__(self):        return self     def __exit__(self, *args):        self.close()     #    # User visible methods.    #    def getfp(self):        return self._file     def rewind(self):        self._ssnd_seek_needed = 1        self._soundpos = 0     def close(self):        file = self._file        if file is not None:            self._file = None            file.close()     def tell(self):        return self._soundpos     def getnchannels(self):        return self._nchannels     def getnframes(self):        return self._nframes     def getsampwidth(self):        return self._sampwidth     def getframerate(self):        return self._framerate     def getcomptype(self):        return self._comptype     def getcompname(self):        return self._compname ##  def getversion(self):##      return self._version     def getparams(self):        return _aifc_params(self.getnchannels(), self.getsampwidth(),                            self.getframerate(), self.getnframes(),                            self.getcomptype(), self.getcompname())     def getmarkers(self):        if len(self._markers) == 0:            return None        return self._markers     def getmark(self, id):        for marker in self._markers:            if id == marker[0]:                return marker        raise Error('marker {0!r} does not exist'.format(id))     def setpos(self, pos):        if pos < 0 or pos > self._nframes:            raise Error('position not in range')        self._soundpos = pos        self._ssnd_seek_needed = 1     def readframes(self, nframes):        if self._ssnd_seek_needed:            self._ssnd_chunk.seek(0)            dummy = self._ssnd_chunk.read(8)            pos = self._soundpos * self._framesize            if pos:                self._ssnd_chunk.seek(pos + 8)            self._ssnd_seek_needed = 0        if nframes == 0:            return b''        data = self._ssnd_chunk.read(nframes * self._framesize)        if self._convert and data:            data = self._convert(data)        self._soundpos = self._soundpos + len(data) // (self._nchannels                                                        * self._sampwidth)        return data     #    # Internal methods.    #     def _alaw2lin(self, data):        import audioop        return audioop.alaw2lin(data, 2)     def _ulaw2lin(self, data):        import audioop        return audioop.ulaw2lin(data, 2)     def _adpcm2lin(self, data):        import audioop        if not hasattr(self, '_adpcmstate'):            # first time            self._adpcmstate = None        data, self._adpcmstate = audioop.adpcm2lin(data, 2, self._adpcmstate)        return data     def _read_comm_chunk(self, chunk):        self._nchannels = _read_short(chunk)        self._nframes = _read_long(chunk)        self._sampwidth = (_read_short(chunk) + 7) // 8        self._framerate = int(_read_float(chunk))        if self._sampwidth <= 0:            raise Error('bad sample width')        if self._nchannels <= 0:            raise Error('bad # of channels')        self._framesize = self._nchannels * self._sampwidth        if self._aifc:            #DEBUG: SGI's soundeditor produces a bad size :-(            kludge = 0            if chunk.chunksize == 18:                kludge = 1                warnings.warn('Warning: bad COMM chunk size')                chunk.chunksize = 23            #DEBUG end            self._comptype = chunk.read(4)            #DEBUG start            if kludge:                length = ord(chunk.file.read(1))                if length & 1 == 0:                    length = length + 1                chunk.chunksize = chunk.chunksize + length                chunk.file.seek(-1, 1)            #DEBUG end            self._compname = _read_string(chunk)            if self._comptype != b'NONE':                if self._comptype == b'G722':                    self._convert = self._adpcm2lin                elif self._comptype in (b'ulaw', b'ULAW'):                    self._convert = self._ulaw2lin                elif self._comptype in (b'alaw', b'ALAW'):                    self._convert = self._alaw2lin                else:                    raise Error('unsupported compression type')                self._sampwidth = 2        else:            self._comptype = b'NONE'            self._compname = b'not compressed'     def _readmark(self, chunk):        nmarkers = _read_short(chunk)        # Some files appear to contain invalid counts.        # Cope with this by testing for EOF.        try:            for i in range(nmarkers):                id = _read_short(chunk)                pos = _read_long(chunk)                name = _read_string(chunk)                if pos or name:                    # some files appear to have                    # dummy markers consisting of                    # a position 0 and name ''                    self._markers.append((id, pos, name))        except EOFError:            w = ('Warning: MARK chunk contains only %s marker%s instead of %s' %                 (len(self._markers), '' if len(self._markers) == 1 else 's',                  nmarkers))            warnings.warn(w) class Aifc_write:    # Variables used in this class:    #    # These variables are user settable through appropriate methods    # of this class:    # _file -- the open file with methods write(), close(), tell(), seek()    #       set through the __init__() method    # _comptype -- the AIFF-C compression type ('NONE' in AIFF)    #       set through the setcomptype() or setparams() method    # _compname -- the human-readable AIFF-C compression type    #       set through the setcomptype() or setparams() method    # _nchannels -- the number of audio channels    #       set through the setnchannels() or setparams() method    # _sampwidth -- the number of bytes per audio sample    #       set through the setsampwidth() or setparams() method    # _framerate -- the sampling frequency    #       set through the setframerate() or setparams() method    # _nframes -- the number of audio frames written to the header    #       set through the setnframes() or setparams() method    # _aifc -- whether we're writing an AIFF-C file or an AIFF file    #       set through the aifc() method, reset through the    #       aiff() method    #    # These variables are used internally only:    # _version -- the AIFF-C version number    # _comp -- the compressor from builtin module cl    # _nframeswritten -- the number of audio frames actually written    # _datalength -- the size of the audio samples written to the header    # _datawritten -- the size of the audio samples actually written     _file = None  # Set here since __del__ checks it     def __init__(self, f):        if isinstance(f, str):            file_object = builtins.open(f, 'wb')            try:                self.initfp(file_object)            except:                file_object.close()                raise             # treat .aiff file extensions as non-compressed audio            if f.endswith('.aiff'):                self._aifc = 0        else:            # assume it is an open file object already            self.initfp(f)     def initfp(self, file):        self._file = file        self._version = _AIFC_version        self._comptype = b'NONE'        self._compname = b'not compressed'        self._convert = None        self._nchannels = 0        self._sampwidth = 0        self._framerate = 0        self._nframes = 0        self._nframeswritten = 0        self._datawritten = 0        self._datalength = 0        self._markers = []        self._marklength = 0        self._aifc = 1      # AIFF-C is default     def __del__(self):        self.close()     def __enter__(self):        return self     def __exit__(self, *args):        self.close()     #    # User visible methods.    #    def aiff(self):        if self._nframeswritten:            raise Error('cannot change parameters after starting to write')        self._aifc = 0     def aifc(self):        if self._nframeswritten:            raise Error('cannot change parameters after starting to write')        self._aifc = 1     def setnchannels(self, nchannels):        if self._nframeswritten:            raise Error('cannot change parameters after starting to write')        if nchannels < 1:            raise Error('bad # of channels')        self._nchannels = nchannels     def getnchannels(self):        if not self._nchannels:            raise Error('number of channels not set')        return self._nchannels     def setsampwidth(self, sampwidth):        if self._nframeswritten:            raise Error('cannot change parameters after starting to write')        if sampwidth < 1 or sampwidth > 4:            raise Error('bad sample width')        self._sampwidth = sampwidth     def getsampwidth(self):        if not self._sampwidth:            raise Error('sample width not set')        return self._sampwidth     def setframerate(self, framerate):        if self._nframeswritten:            raise Error('cannot change parameters after starting to write')        if framerate <= 0:            raise Error('bad frame rate')        self._framerate = framerate     def getframerate(self):        if not self._framerate:            raise Error('frame rate not set')        return self._framerate     def setnframes(self, nframes):        if self._nframeswritten:            raise Error('cannot change parameters after starting to write')        self._nframes = nframes     def getnframes(self):        return self._nframeswritten     def setcomptype(self, comptype, compname):        if self._nframeswritten:            raise Error('cannot change parameters after starting to write')        if comptype not in (b'NONE', b'ulaw', b'ULAW',                            b'alaw', b'ALAW', b'G722'):            raise Error('unsupported compression type')        self._comptype = comptype        self._compname = compname     def getcomptype(self):        return self._comptype     def getcompname(self):        return self._compname ##  def setversion(self, version):##      if self._nframeswritten:##          raise Error, 'cannot change parameters after starting to write'##      self._version = version     def setparams(self, params):        nchannels, sampwidth, framerate, nframes, comptype, compname = params        if self._nframeswritten:            raise Error('cannot change parameters after starting to write')        if comptype not in (b'NONE', b'ulaw', b'ULAW',                            b'alaw', b'ALAW', b'G722'):            raise Error('unsupported compression type')        self.setnchannels(nchannels)        self.setsampwidth(sampwidth)        self.setframerate(framerate)        self.setnframes(nframes)        self.setcomptype(comptype, compname)     def getparams(self):        if not self._nchannels or not self._sampwidth or not self._framerate:            raise Error('not all parameters set')        return _aifc_params(self._nchannels, self._sampwidth, self._framerate,                            self._nframes, self._comptype, self._compname)     def setmark(self, id, pos, name):        if id <= 0:            raise Error('marker ID must be > 0')        if pos < 0:            raise Error('marker position must be >= 0')        if not isinstance(name, bytes):            raise Error('marker name must be bytes')        for i in range(len(self._markers)):            if id == self._markers[i][0]:                self._markers[i] = id, pos, name                return        self._markers.append((id, pos, name))     def getmark(self, id):        for marker in self._markers:            if id == marker[0]:                return marker        raise Error('marker {0!r} does not exist'.format(id))     def getmarkers(self):        if len(self._markers) == 0:            return None        return self._markers     def tell(self):        return self._nframeswritten     def writeframesraw(self, data):        if not isinstance(data, (bytes, bytearray)):            data = memoryview(data).cast('B')        self._ensure_header_written(len(data))        nframes = len(data) // (self._sampwidth * self._nchannels)        if self._convert:            data = self._convert(data)        self._file.write(data)        self._nframeswritten = self._nframeswritten + nframes        self._datawritten = self._datawritten + len(data)     def writeframes(self, data):        self.writeframesraw(data)        if self._nframeswritten != self._nframes or \              self._datalength != self._datawritten:            self._patchheader()     def close(self):        if self._file is None:            return        try:            self._ensure_header_written(0)            if self._datawritten & 1:                # quick pad to even size                self._file.write(b'\x00')                self._datawritten = self._datawritten + 1            self._writemarkers()            if self._nframeswritten != self._nframes or \                  self._datalength != self._datawritten or \                  self._marklength:                self._patchheader()        finally:            # Prevent ref cycles            self._convert = None            f = self._file            self._file = None            f.close()     #    # Internal methods.    #     def _lin2alaw(self, data):        import audioop        return audioop.lin2alaw(data, 2)     def _lin2ulaw(self, data):        import audioop        return audioop.lin2ulaw(data, 2)     def _lin2adpcm(self, data):        import audioop        if not hasattr(self, '_adpcmstate'):            self._adpcmstate = None        data, self._adpcmstate = audioop.lin2adpcm(data, 2, self._adpcmstate)        return data     def _ensure_header_written(self, datasize):        if not self._nframeswritten:            if self._comptype in (b'ULAW', b'ulaw', b'ALAW', b'alaw', b'G722'):                if not self._sampwidth:                    self._sampwidth = 2                if self._sampwidth != 2:                    raise Error('sample width must be 2 when compressing '                                'with ulaw/ULAW, alaw/ALAW or G7.22 (ADPCM)')            if not self._nchannels:                raise Error('# channels not specified')            if not self._sampwidth:                raise Error('sample width not specified')            if not self._framerate:                raise Error('sampling rate not specified')            self._write_header(datasize)     def _init_compression(self):        if self._comptype == b'G722':            self._convert = self._lin2adpcm        elif self._comptype in (b'ulaw', b'ULAW'):            self._convert = self._lin2ulaw        elif self._comptype in (b'alaw', b'ALAW'):            self._convert = self._lin2alaw     def _write_header(self, initlength):        if self._aifc and self._comptype != b'NONE':            self._init_compression()        self._file.write(b'FORM')        if not self._nframes:            self._nframes = initlength // (self._nchannels * self._sampwidth)        self._datalength = self._nframes * self._nchannels * self._sampwidth        if self._datalength & 1:            self._datalength = self._datalength + 1        if self._aifc:            if self._comptype in (b'ulaw', b'ULAW', b'alaw', b'ALAW'):                self._datalength = self._datalength // 2                if self._datalength & 1:                    self._datalength = self._datalength + 1            elif self._comptype == b'G722':                self._datalength = (self._datalength + 3) // 4                if self._datalength & 1:                    self._datalength = self._datalength + 1        try:            self._form_length_pos = self._file.tell()        except (AttributeError, OSError):            self._form_length_pos = None        commlength = self._write_form_length(self._datalength)        if self._aifc:            self._file.write(b'AIFC')            self._file.write(b'FVER')            _write_ulong(self._file, 4)            _write_ulong(self._file, self._version)        else:            self._file.write(b'AIFF')        self._file.write(b'COMM')        _write_ulong(self._file, commlength)        _write_short(self._file, self._nchannels)        if self._form_length_pos is not None:            self._nframes_pos = self._file.tell()        _write_ulong(self._file, self._nframes)        if self._comptype in (b'ULAW', b'ulaw', b'ALAW', b'alaw', b'G722'):            _write_short(self._file, 8)        else:            _write_short(self._file, self._sampwidth * 8)        _write_float(self._file, self._framerate)        if self._aifc:            self._file.write(self._comptype)            _write_string(self._file, self._compname)        self._file.write(b'SSND')        if self._form_length_pos is not None:            self._ssnd_length_pos = self._file.tell()        _write_ulong(self._file, self._datalength + 8)        _write_ulong(self._file, 0)        _write_ulong(self._file, 0)     def _write_form_length(self, datalength):        if self._aifc:            commlength = 18 + 5 + len(self._compname)            if commlength & 1:                commlength = commlength + 1            verslength = 12        else:            commlength = 18            verslength = 0        _write_ulong(self._file, 4 + verslength + self._marklength + \                     8 + commlength + 16 + datalength)        return commlength     def _patchheader(self):        curpos = self._file.tell()        if self._datawritten & 1:            datalength = self._datawritten + 1            self._file.write(b'\x00')        else:            datalength = self._datawritten        if datalength == self._datalength and \              self._nframes == self._nframeswritten and \              self._marklength == 0:            self._file.seek(curpos, 0)            return        self._file.seek(self._form_length_pos, 0)        dummy = self._write_form_length(datalength)        self._file.seek(self._nframes_pos, 0)        _write_ulong(self._file, self._nframeswritten)        self._file.seek(self._ssnd_length_pos, 0)        _write_ulong(self._file, datalength + 8)        self._file.seek(curpos, 0)        self._nframes = self._nframeswritten        self._datalength = datalength     def _writemarkers(self):        if len(self._markers) == 0:            return        self._file.write(b'MARK')        length = 2        for marker in self._markers:            id, pos, name = marker            length = length + len(name) + 1 + 6            if len(name) & 1 == 0:                length = length + 1        _write_ulong(self._file, length)        self._marklength = length + 8        _write_short(self._file, len(self._markers))        for marker in self._markers:            id, pos, name = marker            _write_short(self._file, id)            _write_ulong(self._file, pos)            _write_string(self._file, name) def open(f, mode=None):    if mode is None:        if hasattr(f, 'mode'):            mode = f.mode        else:            mode = 'rb'    if mode in ('r', 'rb'):        return Aifc_read(f)    elif mode in ('w', 'wb'):        return Aifc_write(f)    else:        raise Error("mode must be 'r', 'rb', 'w', or 'wb'")  if __name__ == '__main__':    import sys    if not sys.argv[1:]:        sys.argv.append('/usr/demos/data/audio/bach.aiff')    fn = sys.argv[1]    with open(fn, 'r') as f:        print("Reading", fn)        print("nchannels =", f.getnchannels())        print("nframes   =", f.getnframes())        print("sampwidth =", f.getsampwidth())        print("framerate =", f.getframerate())        print("comptype  =", f.getcomptype())        print("compname  =", f.getcompname())        if sys.argv[2:]:            gn = sys.argv[2]            print("Writing", gn)            with open(gn, 'w') as g:                g.setparams(f.getparams())                while 1:                    data = f.readframes(1024)                    if not data:                        break                    g.writeframes(data)            print("Done.")