2 :mod:`aifc` --- Read and write AIFF and AIFC files
3 ==================================================
6 :synopsis: Read and write audio files in AIFF or AIFC format.
10 single: Audio Interchange File Format
14 This module provides support for reading and writing AIFF and AIFF-C files.
15 AIFF is Audio Interchange File Format, a format for storing digital audio
16 samples in a file. AIFF-C is a newer version of the format that includes the
17 ability to compress the audio data.
21 Some operations may only work under IRIX; these will raise :exc:`ImportError`
22 when attempting to import the :mod:`cl` module, which is only available on IRIX.
24 Audio files have a number of parameters that describe the audio data. The
25 sampling rate or frame rate is the number of times per second the sound is
26 sampled. The number of channels indicate if the audio is mono, stereo, or
27 quadro. Each frame consists of one sample per channel. The sample size is the
28 size in bytes of each sample. Thus a frame consists of
29 *nchannels*\**samplesize* bytes, and a second's worth of audio consists of
30 *nchannels*\**samplesize*\**framerate* bytes.
32 For example, CD quality audio has a sample size of two bytes (16 bits), uses two
33 channels (stereo) and has a frame rate of 44,100 frames/second. This gives a
34 frame size of 4 bytes (2\*2), and a second's worth occupies 2\*2\*44100 bytes
37 Module :mod:`aifc` defines the following function:
40 .. function:: open(file[, mode])
42 Open an AIFF or AIFF-C file and return an object instance with methods that are
43 described below. The argument *file* is either a string naming a file or a file
44 object. *mode* must be ``'r'`` or ``'rb'`` when the file must be opened for
45 reading, or ``'w'`` or ``'wb'`` when the file must be opened for writing. If
46 omitted, ``file.mode`` is used if it exists, otherwise ``'rb'`` is used. When
47 used for writing, the file object should be seekable, unless you know ahead of
48 time how many samples you are going to write in total and use
49 :meth:`writeframesraw` and :meth:`setnframes`.
51 Objects returned by :func:`open` when a file is opened for reading have the
55 .. method:: aifc.getnchannels()
57 Return the number of audio channels (1 for mono, 2 for stereo).
60 .. method:: aifc.getsampwidth()
62 Return the size in bytes of individual samples.
65 .. method:: aifc.getframerate()
67 Return the sampling rate (number of audio frames per second).
70 .. method:: aifc.getnframes()
72 Return the number of audio frames in the file.
75 .. method:: aifc.getcomptype()
77 Return a four-character string describing the type of compression used in the
78 audio file. For AIFF files, the returned value is ``'NONE'``.
81 .. method:: aifc.getcompname()
83 Return a human-readable description of the type of compression used in the audio
84 file. For AIFF files, the returned value is ``'not compressed'``.
87 .. method:: aifc.getparams()
89 Return a tuple consisting of all of the above values in the above order.
92 .. method:: aifc.getmarkers()
94 Return a list of markers in the audio file. A marker consists of a tuple of
95 three elements. The first is the mark ID (an integer), the second is the mark
96 position in frames from the beginning of the data (an integer), the third is the
97 name of the mark (a string).
100 .. method:: aifc.getmark(id)
102 Return the tuple as described in :meth:`getmarkers` for the mark with the given
106 .. method:: aifc.readframes(nframes)
108 Read and return the next *nframes* frames from the audio file. The returned
109 data is a string containing for each frame the uncompressed samples of all
113 .. method:: aifc.rewind()
115 Rewind the read pointer. The next :meth:`readframes` will start from the
119 .. method:: aifc.setpos(pos)
121 Seek to the specified frame number.
124 .. method:: aifc.tell()
126 Return the current frame number.
129 .. method:: aifc.close()
131 Close the AIFF file. After calling this method, the object can no longer be
134 Objects returned by :func:`open` when a file is opened for writing have all the
135 above methods, except for :meth:`readframes` and :meth:`setpos`. In addition
136 the following methods exist. The :meth:`get\*` methods can only be called after
137 the corresponding :meth:`set\*` methods have been called. Before the first
138 :meth:`writeframes` or :meth:`writeframesraw`, all parameters except for the
139 number of frames must be filled in.
142 .. method:: aifc.aiff()
144 Create an AIFF file. The default is that an AIFF-C file is created, unless the
145 name of the file ends in ``'.aiff'`` in which case the default is an AIFF file.
148 .. method:: aifc.aifc()
150 Create an AIFF-C file. The default is that an AIFF-C file is created, unless
151 the name of the file ends in ``'.aiff'`` in which case the default is an AIFF
155 .. method:: aifc.setnchannels(nchannels)
157 Specify the number of channels in the audio file.
160 .. method:: aifc.setsampwidth(width)
162 Specify the size in bytes of audio samples.
165 .. method:: aifc.setframerate(rate)
167 Specify the sampling frequency in frames per second.
170 .. method:: aifc.setnframes(nframes)
172 Specify the number of frames that are to be written to the audio file. If this
173 parameter is not set, or not set correctly, the file needs to support seeking.
176 .. method:: aifc.setcomptype(type, name)
183 Specify the compression type. If not specified, the audio data will not be
184 compressed. In AIFF files, compression is not possible. The name parameter
185 should be a human-readable description of the compression type, the type
186 parameter should be a four-character string. Currently the following
187 compression types are supported: NONE, ULAW, ALAW, G722.
190 .. method:: aifc.setparams(nchannels, sampwidth, framerate, comptype, compname)
192 Set all the above parameters at once. The argument is a tuple consisting of the
193 various parameters. This means that it is possible to use the result of a
194 :meth:`getparams` call as argument to :meth:`setparams`.
197 .. method:: aifc.setmark(id, pos, name)
199 Add a mark with the given id (larger than 0), and the given name at the given
200 position. This method can be called at any time before :meth:`close`.
203 .. method:: aifc.tell()
205 Return the current write position in the output file. Useful in combination
206 with :meth:`setmark`.
209 .. method:: aifc.writeframes(data)
211 Write data to the output file. This method can only be called after the audio
212 file parameters have been set.
215 .. method:: aifc.writeframesraw(data)
217 Like :meth:`writeframes`, except that the header of the audio file is not
221 .. method:: aifc.close()
223 Close the AIFF file. The header of the file is updated to reflect the actual
224 size of the audio data. After calling this method, the object can no longer be