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263 lines
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ReStructuredText
263 lines
7 KiB
ReStructuredText
:mod:`sunau` --- Read and write Sun AU files
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============================================
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.. module:: sunau
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:synopsis: Provide an interface to the Sun AU sound format.
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.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
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**Source code:** :source:`Lib/sunau.py`
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--------------
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The :mod:`sunau` module provides a convenient interface to the Sun AU sound
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format. Note that this module is interface-compatible with the modules
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:mod:`aifc` and :mod:`wave`.
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An audio file consists of a header followed by the data. The fields of the
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header are:
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+---------------+-----------------------------------------------+
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| Field | Contents |
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+===============+===============================================+
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| magic word | The four bytes ``.snd``. |
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+---------------+-----------------------------------------------+
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| header size | Size of the header, including info, in bytes. |
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+---------------+-----------------------------------------------+
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| data size | Physical size of the data, in bytes. |
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+---------------+-----------------------------------------------+
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| encoding | Indicates how the audio samples are encoded. |
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+---------------+-----------------------------------------------+
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| sample rate | The sampling rate. |
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+---------------+-----------------------------------------------+
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| # of channels | The number of channels in the samples. |
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+---------------+-----------------------------------------------+
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| info | ASCII string giving a description of the |
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| | audio file (padded with null bytes). |
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+---------------+-----------------------------------------------+
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Apart from the info field, all header fields are 4 bytes in size. They are all
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32-bit unsigned integers encoded in big-endian byte order.
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The :mod:`sunau` module defines the following functions:
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.. function:: open(file, mode)
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If *file* is a string, open the file by that name, otherwise treat it as a
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seekable file-like object. *mode* can be any of
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``'r'``
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Read only mode.
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``'w'``
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Write only mode.
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Note that it does not allow read/write files.
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A *mode* of ``'r'`` returns a :class:`AU_read` object, while a *mode* of ``'w'``
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or ``'wb'`` returns a :class:`AU_write` object.
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.. function:: openfp(file, mode)
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A synonym for :func:`.open`, maintained for backwards compatibility.
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The :mod:`sunau` module defines the following exception:
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.. exception:: Error
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An error raised when something is impossible because of Sun AU specs or
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implementation deficiency.
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The :mod:`sunau` module defines the following data items:
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.. data:: AUDIO_FILE_MAGIC
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An integer every valid Sun AU file begins with, stored in big-endian form. This
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is the string ``.snd`` interpreted as an integer.
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.. data:: AUDIO_FILE_ENCODING_MULAW_8
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AUDIO_FILE_ENCODING_LINEAR_8
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AUDIO_FILE_ENCODING_LINEAR_16
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AUDIO_FILE_ENCODING_LINEAR_24
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AUDIO_FILE_ENCODING_LINEAR_32
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AUDIO_FILE_ENCODING_ALAW_8
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Values of the encoding field from the AU header which are supported by this
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module.
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.. data:: AUDIO_FILE_ENCODING_FLOAT
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AUDIO_FILE_ENCODING_DOUBLE
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AUDIO_FILE_ENCODING_ADPCM_G721
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AUDIO_FILE_ENCODING_ADPCM_G722
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AUDIO_FILE_ENCODING_ADPCM_G723_3
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AUDIO_FILE_ENCODING_ADPCM_G723_5
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Additional known values of the encoding field from the AU header, but which are
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not supported by this module.
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.. _au-read-objects:
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AU_read Objects
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---------------
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AU_read objects, as returned by :func:`.open` above, have the following methods:
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.. method:: AU_read.close()
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Close the stream, and make the instance unusable. (This is called automatically
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on deletion.)
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.. method:: AU_read.getnchannels()
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Returns number of audio channels (1 for mone, 2 for stereo).
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.. method:: AU_read.getsampwidth()
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Returns sample width in bytes.
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.. method:: AU_read.getframerate()
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Returns sampling frequency.
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.. method:: AU_read.getnframes()
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Returns number of audio frames.
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.. method:: AU_read.getcomptype()
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Returns compression type. Supported compression types are ``'ULAW'``, ``'ALAW'``
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and ``'NONE'``.
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.. method:: AU_read.getcompname()
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Human-readable version of :meth:`getcomptype`. The supported types have the
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respective names ``'CCITT G.711 u-law'``, ``'CCITT G.711 A-law'`` and ``'not
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compressed'``.
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.. method:: AU_read.getparams()
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Returns a tuple ``(nchannels, sampwidth, framerate, nframes, comptype,
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compname)``, equivalent to output of the :meth:`get\*` methods.
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.. method:: AU_read.readframes(n)
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Reads and returns at most *n* frames of audio, as a string of bytes. The data
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will be returned in linear format. If the original data is in u-LAW format, it
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will be converted.
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.. method:: AU_read.rewind()
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Rewind the file pointer to the beginning of the audio stream.
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The following two methods define a term "position" which is compatible between
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them, and is otherwise implementation dependent.
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.. method:: AU_read.setpos(pos)
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Set the file pointer to the specified position. Only values returned from
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:meth:`tell` should be used for *pos*.
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.. method:: AU_read.tell()
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Return current file pointer position. Note that the returned value has nothing
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to do with the actual position in the file.
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The following two functions are defined for compatibility with the :mod:`aifc`,
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and don't do anything interesting.
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.. method:: AU_read.getmarkers()
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Returns ``None``.
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.. method:: AU_read.getmark(id)
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Raise an error.
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.. _au-write-objects:
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AU_write Objects
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----------------
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AU_write objects, as returned by :func:`.open` above, have the following methods:
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.. method:: AU_write.setnchannels(n)
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Set the number of channels.
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.. method:: AU_write.setsampwidth(n)
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Set the sample width (in bytes.)
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.. method:: AU_write.setframerate(n)
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Set the frame rate.
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.. method:: AU_write.setnframes(n)
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Set the number of frames. This can be later changed, when and if more frames
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are written.
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.. method:: AU_write.setcomptype(type, name)
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Set the compression type and description. Only ``'NONE'`` and ``'ULAW'`` are
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supported on output.
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.. method:: AU_write.setparams(tuple)
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The *tuple* should be ``(nchannels, sampwidth, framerate, nframes, comptype,
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compname)``, with values valid for the :meth:`set\*` methods. Set all
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parameters.
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.. method:: AU_write.tell()
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Return current position in the file, with the same disclaimer for the
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:meth:`AU_read.tell` and :meth:`AU_read.setpos` methods.
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.. method:: AU_write.writeframesraw(data)
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Write audio frames, without correcting *nframes*.
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.. method:: AU_write.writeframes(data)
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Write audio frames and make sure *nframes* is correct.
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.. method:: AU_write.close()
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Make sure *nframes* is correct, and close the file.
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This method is called upon deletion.
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Note that it is invalid to set any parameters after calling :meth:`writeframes`
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or :meth:`writeframesraw`.
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