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author | Georg Brandl <georg@python.org> | 2007-08-15 14:28:22 (GMT) |
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committer | Georg Brandl <georg@python.org> | 2007-08-15 14:28:22 (GMT) |
commit | 116aa62bf54a39697e25f21d6cf6799f7faa1349 (patch) | |
tree | 8db5729518ed4ca88e26f1e26cc8695151ca3eb3 /Doc/library/aifc.rst | |
parent | 739c01d47b9118d04e5722333f0e6b4d0c8bdd9e (diff) | |
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diff --git a/Doc/library/aifc.rst b/Doc/library/aifc.rst new file mode 100644 index 0000000..0cfcb52 --- /dev/null +++ b/Doc/library/aifc.rst @@ -0,0 +1,225 @@ + +: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 AIFF-C is a newer version of the format that includes the +ability to compress the audio data.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. + |