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authorGeorg Brandl <georg@python.org>2007-08-15 14:28:22 (GMT)
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+
+:mod:`aifc` --- Read and write AIFF and AIFC files
+==================================================
+
+.. module:: aifc
+ :synopsis: Read and write audio files in AIFF or AIFC format.
+
+
+.. index::
+ single: Audio Interchange File Format
+ single: AIFF
+ single: AIFF-C
+
+This module provides support for reading and writing AIFF and AIFF-C files.
+AIFF is Audio Interchange File Format, a format for storing digital audio
+samples in a file. AIFF-C is a newer version of the format that includes the
+ability to compress the audio data.
+
+**Caveat:** Some operations may only work under IRIX; these will raise
+:exc:`ImportError` when attempting to import the :mod:`cl` module, which is only
+available on IRIX.
+
+Audio files have a number of parameters that describe the audio data. The
+sampling rate or frame rate is the number of times per second the sound is
+sampled. The number of channels indicate if the audio is mono, stereo, or
+quadro. Each frame consists of one sample per channel. The sample size is the
+size in bytes of each sample. Thus a frame consists of
+*nchannels*\**samplesize* bytes, and a second's worth of audio consists of
+*nchannels*\**samplesize*\**framerate* bytes.
+
+For example, CD quality audio has a sample size of two bytes (16 bits), uses two
+channels (stereo) and has a frame rate of 44,100 frames/second. This gives a
+frame size of 4 bytes (2\*2), and a second's worth occupies 2\*2\*44100 bytes
+(176,400 bytes).
+
+Module :mod:`aifc` defines the following function:
+
+
+.. function:: open(file[, mode])
+
+ Open an AIFF or AIFF-C file and return an object instance with methods that are
+ described below. The argument *file* is either a string naming a file or a file
+ object. *mode* must be ``'r'`` or ``'rb'`` when the file must be opened for
+ reading, or ``'w'`` or ``'wb'`` when the file must be opened for writing. If
+ omitted, ``file.mode`` is used if it exists, otherwise ``'rb'`` is used. When
+ used for writing, the file object should be seekable, unless you know ahead of
+ time how many samples you are going to write in total and use
+ :meth:`writeframesraw` and :meth:`setnframes`.
+
+Objects returned by :func:`open` when a file is opened for reading have the
+following methods:
+
+
+.. method:: aifc.getnchannels()
+
+ Return the number of audio channels (1 for mono, 2 for stereo).
+
+
+.. method:: aifc.getsampwidth()
+
+ Return the size in bytes of individual samples.
+
+
+.. method:: aifc.getframerate()
+
+ Return the sampling rate (number of audio frames per second).
+
+
+.. method:: aifc.getnframes()
+
+ Return the number of audio frames in the file.
+
+
+.. method:: aifc.getcomptype()
+
+ Return a four-character string describing the type of compression used in the
+ audio file. For AIFF files, the returned value is ``'NONE'``.
+
+
+.. method:: aifc.getcompname()
+
+ Return a human-readable description of the type of compression used in the audio
+ file. For AIFF files, the returned value is ``'not compressed'``.
+
+
+.. method:: aifc.getparams()
+
+ Return a tuple consisting of all of the above values in the above order.
+
+
+.. method:: aifc.getmarkers()
+
+ Return a list of markers in the audio file. A marker consists of a tuple of
+ three elements. The first is the mark ID (an integer), the second is the mark
+ position in frames from the beginning of the data (an integer), the third is the
+ name of the mark (a string).
+
+
+.. method:: aifc.getmark(id)
+
+ Return the tuple as described in :meth:`getmarkers` for the mark with the given
+ *id*.
+
+
+.. method:: aifc.readframes(nframes)
+
+ Read and return the next *nframes* frames from the audio file. The returned
+ data is a string containing for each frame the uncompressed samples of all
+ channels.
+
+
+.. method:: aifc.rewind()
+
+ Rewind the read pointer. The next :meth:`readframes` will start from the
+ beginning.
+
+
+.. method:: aifc.setpos(pos)
+
+ Seek to the specified frame number.
+
+
+.. method:: aifc.tell()
+
+ Return the current frame number.
+
+
+.. method:: aifc.close()
+
+ Close the AIFF file. After calling this method, the object can no longer be
+ used.
+
+Objects returned by :func:`open` when a file is opened for writing have all the
+above methods, except for :meth:`readframes` and :meth:`setpos`. In addition
+the following methods exist. The :meth:`get\*` methods can only be called after
+the corresponding :meth:`set\*` methods have been called. Before the first
+:meth:`writeframes` or :meth:`writeframesraw`, all parameters except for the
+number of frames must be filled in.
+
+
+.. method:: aifc.aiff()
+
+ Create an AIFF file. The default is that an AIFF-C file is created, unless the
+ name of the file ends in ``'.aiff'`` in which case the default is an AIFF file.
+
+
+.. method:: aifc.aifc()
+
+ Create an AIFF-C file. The default is that an AIFF-C file is created, unless
+ the name of the file ends in ``'.aiff'`` in which case the default is an AIFF
+ file.
+
+
+.. method:: aifc.setnchannels(nchannels)
+
+ Specify the number of channels in the audio file.
+
+
+.. method:: aifc.setsampwidth(width)
+
+ Specify the size in bytes of audio samples.
+
+
+.. method:: aifc.setframerate(rate)
+
+ Specify the sampling frequency in frames per second.
+
+
+.. method:: aifc.setnframes(nframes)
+
+ Specify the number of frames that are to be written to the audio file. If this
+ parameter is not set, or not set correctly, the file needs to support seeking.
+
+
+.. method:: aifc.setcomptype(type, name)
+
+ .. index::
+ single: u-LAW
+ single: A-LAW
+ single: G.722
+
+ Specify the compression type. If not specified, the audio data will not be
+ compressed. In AIFF files, compression is not possible. The name parameter
+ should be a human-readable description of the compression type, the type
+ parameter should be a four-character string. Currently the following
+ compression types are supported: NONE, ULAW, ALAW, G722.
+
+
+.. method:: aifc.setparams(nchannels, sampwidth, framerate, comptype, compname)
+
+ Set all the above parameters at once. The argument is a tuple consisting of the
+ various parameters. This means that it is possible to use the result of a
+ :meth:`getparams` call as argument to :meth:`setparams`.
+
+
+.. method:: aifc.setmark(id, pos, name)
+
+ Add a mark with the given id (larger than 0), and the given name at the given
+ position. This method can be called at any time before :meth:`close`.
+
+
+.. method:: aifc.tell()
+
+ Return the current write position in the output file. Useful in combination
+ with :meth:`setmark`.
+
+
+.. method:: aifc.writeframes(data)
+
+ Write data to the output file. This method can only be called after the audio
+ file parameters have been set.
+
+
+.. method:: aifc.writeframesraw(data)
+
+ Like :meth:`writeframes`, except that the header of the audio file is not
+ updated.
+
+
+.. method:: aifc.close()
+
+ Close the AIFF file. The header of the file is updated to reflect the actual
+ size of the audio data. After calling this method, the object can no longer be
+ used.
+