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