\section{\module{ossaudiodev} --- Access to OSS-compatible audio devices} \declaremodule{builtin}{ossaudiodev} \platform{Linux, FreeBSD} \modulesynopsis{Access to OSS-compatible audio devices.} % XXX OSS is standard for Linux and FreeBSD -- what about NetBSD? % OpenBSD? others? This module allows you to access the OSS (Open Sound System) audio interface. OSS is available for a wide range of open-source and commercial Unices, and is the standard audio interface for Linux (up to kernel 2.4) and FreeBSD. \begin{seealso} \seetitle[http://www.opensound.com/pguide/oss.pdf] {Open Sound System Programmer's Guide} {the official documentation for the OSS C API} \seetext{The module defines a large number of constants supplied by the OSS device driver; see \file{} on either Linux or FreeBSD for a listing .} \end{seealso} \module{ossaudiodev} defines the following variables and functions: \begin{excdesc}{error} This exception is raised on certain errors. The argument is a string describing what went wrong. (If \module{ossaudiodev} receives an error from a system call such as \cfunction{open()}, \cfunction{write()}, or \cfunction{ioctl()}, it raises \exception{IOError}. Errors detected directly by \module{ossaudiodev} result in \exception{ossaudiodev.error}.) \end{excdesc} \begin{funcdesc}{open}{\optional{device, }mode} Open an audio device and return an OSS audio device object. This object supports many file-like methods, such as \method{read()}, \method{write()}, and \method{fileno()} (although there are subtle differences between conventional Unix read/write semantics and those of OSS audio devices). It also supports a number of audio-specific methods; see below for the complete list of methods. Note the unusual calling syntax: the \emph{first} argument is optional, and the second is required. This is a historical artifact for compatibility with the older \module{linuxaudiodev} module which \module{ossaudiodev} supersedes. % XXX it might also be motivated % by my unfounded-but-still-possibly-true belief that the default % audio device varies unpredictably across operating systems. -GW \var{device} is the audio device filename to use. If it is not specified, this module first looks in the environment variable \envvar{AUDIODEV} for a device to use. If not found, it falls back to \file{/dev/dsp}. \var{mode} is one of \code{'r'} for read-only (record) access, \code{'w'} for write-only (playback) access and \code{'rw'} for both. Since many soundcards only allow one process to have the recorder or player open at a time it is a good idea to open the device only for the activity needed. Further, some soundcards are half-duplex: they can be opened for reading or writing, but not both at once. \end{funcdesc} \begin{funcdesc}{openmixer}{\optional{device}} Open a mixer device and return an OSS mixer device object. \var{device} is the mixer device filename to use. If it is not specified, this module first looks in the environment variable \envvar{MIXERDEV} for a device to use. If not found, it falls back to \file{/dev/mixer}. \end{funcdesc} \subsection{Audio Device Objects \label{ossaudio-device-objects}} Setting up the device To set up the device, three functions must be called in the correct sequence: \begin{enumerate} \item \method{setfmt()} to set the output format, \item \method{channels()} to set the number of channels, and \item \method{speed()} to set the sample rate. \end{enumerate} The audio device objects are returned by \function{open()} define the following methods: \begin{methoddesc}[audio device]{close}{} This method explicitly closes the device. It is useful in situations where deleting the object does not immediately close it since there are other references to it. A closed device should not be used again. \end{methoddesc} \begin{methoddesc}[audio device]{fileno}{} Returns the file descriptor associated with the device. \end{methoddesc} \begin{methoddesc}[audio device]{read}{size} Reads \var{size} samples from the audio input and returns them as a Python string. The function blocks until enough data is available. \end{methoddesc} \begin{methoddesc}[audio device]{write}{data} Writes Python string \var{data} to the audio device and returns the number of bytes written. If the audio device is opened in blocking mode, the entire string is always written. If the device is opened in nonblocking mode, some data may not be written---see \method{writeall()}. \end{methoddesc} \begin{methoddesc}[audio device]{writeall}{data} Writes the entire Python string \var{data} to the audio device. If the device is opened in blocking mode, behaves identially to \method{write()}; in nonblocking mode, waits until the device becomes available before feeding it more data. Returns \code{None}, since the amount of data written is always equal to the amount of data supplied. \end{methoddesc} Simple IOCTLs: \begin{methoddesc}[audio device]{nonblock}{} Attempts to put the device into nonblocking mode. Once in nonblocking mode there is no way to return to blocking mode. Raises \exception{IOError} if the IOCTL failed. \end{methoddesc} \begin{methoddesc}[audio device]{getfmts}{} Returns a bitmask of the audio output formats supported by the soundcard. On a typical Linux system, these formats are: \begin{tableii}{l|l}{constant}{Format}{Description} \lineii{AFMT_MU_LAW} {a logarithmic encoding. This is the default format on \file{/dev/audio} and is the format used by Sun .au files.} \lineii{AFMT_A_LAW} {a logarithmic encoding} \lineii{AFMT_IMA_ADPCM} {a 4:1 compressed format defined by the Interactive Multimedia Association.} \lineii{AFMT_U8} {Unsigned, 8-bit audio.} \lineii{AFMT_S16_LE} {Unsigned, 16-bit audio, little-endian byte order (as used by Intel processors)} \lineii{AFMT_S16_BE} {Unsigned, 16-bit audio, big-endian byte order (as used by 68k, PowerPC, Sparc)} \lineii{AFMT_S8} {Signed, 8 bit audio.} \lineii{AFMT_U16_LE} {Signed, 16-bit little-endian audio} \lineii{AFMT_U16_BE} {Signed, 16-bit big-endian audio} \end{tableii} Most systems support only a subset of these formats. Many devices only support \constant{AFMT_U8}; the most common format used today is \constant{AFMT_S16_LE}. \end{methoddesc} \begin{methoddesc}[audio device]{setfmt}{format} Used to set the current audio format to \var{format}---see \method{getfmts()} for a list. May also be used to return the current audio format---do this by passing an ``audio format'' of \constant{AFMT_QUERY}. Returns the audio format that the device was set to, which may not be the requested format. \end{methoddesc} \begin{methoddesc}[audio device]{channels}{num_channels} Sets the number of output channels to \var{num_channels}. A value of 1 indicates monophonic sound, 2 stereophonic. Some devices may have more than 2 channels, and some high-end devices may not support mono. Returns the number of channels the device was set to. \end{methoddesc} \begin{methoddesc}[audio device]{speed}{samplerate} Sets the samplerate to \var{samplerate} samples per second and returns the rate actually set. Most sound devices don't support arbitrary sample rates. Common rates are: 8000---default rate 11025---speech recording 22050 44100---Audio CD-quality (at 16 bits/sample and 2 channels) 96000---DVD-quality \end{methoddesc} \begin{methoddesc}[audio device]{sync} Waits until the sound device has played every byte in its buffer and returns. This also occurs when the sound device is closed. The OSS documentation recommends simply closing and re-opening the device rather than using \method{sync()}. \end{methoddesc} \begin{methoddesc}[audio device]{reset} Immediately stops and playing or recording and returns the device to a state where it can accept commands. The OSS documentation recommends closing and re-opening the device after calling \method{reset()}. \end{methoddesc} \begin{methoddesc}[audio device]{post} To be used like a lightweight \method{sync()}, the \method{post()} IOCTL informs the audio device that there is a likely to be a pause in the audio output---i.e., after playing a spot sound effect, before waiting for user input, or before doing disk I/O. \end{methoddesc} Convenience methods \begin{methoddesc}[audio device]{setparameters}{samplerate,num_channels,format,emulate} Initialise the sound device in one method. \var{samplerate}, \var{channels} and \var{format} should be as specified in the \method{speed()}, \method{channels()} and \method{setfmt()} methods. If \var{emulate} is true, attempt to find the closest matching format instead, otherwise raise ValueError if the device does not support the format. The default is to raise ValueError on unsupported formats. \end{methoddesc} \begin{methoddesc}[audio device]{bufsize}{} Returns the size of the hardware buffer, in samples. \end{methoddesc} \begin{methoddesc}[audio device]{obufcount}{} Returns the number of samples that are in the hardware buffer yet to be played. \end{methoddesc} \begin{methoddesc}[audio device]{obuffree}{} Returns the number of samples that could be queued into the hardware buffer to be played without blocking. \end{methoddesc} \subsection{Mixer Device Objects \label{mixer-device-objects}} File-like interface \begin{methoddesc}[mixer device]{close}{} This method closes the open mixer device file. Any further attempts to use the mixer after this file is closed will raise an IOError. \end{methoddesc} \begin{methoddesc}[mixer device]{fileno}{} Returns the file handle number of the open mixer device file. \end{methoddesc} Mixer interface \begin{methoddesc}[mixer device]{controls}{} This method returns a bitmask specifying the available mixer controls (``Control'' being a specific mixable ``channel'', such as \constant{SOUND_MIXER_PCM} or \constant{SOUND_MIXER_SYNTH}). This bitmask indicates a subset of all available mixer channels---the \constant{SOUND_MIXER_*} constants defined at module level. To determine if, for example, the current mixer object supports a PCM mixer, use the following Python code: \begin{verbatim} mixer=ossaudiodev.openmixer() if mixer.channels() & (1 << ossaudiodev.SOUND_MIXER_PCM): # PCM is supported \end{verbatim} For most purposes, the \constant{SOUND_MIXER_VOLUME} (Master volume) and \constant{SOUND_MIXER_PCM} channels should suffice---but code that uses the mixer should be flexible when it comes to choosing sound channels. On the Gravis Ultrasound, for example, \constant{SOUND_MIXER_VOLUME} does not exist. \end{methoddesc} \begin{methoddesc}[mixer device]{stereocontrols}{} Returns a bitmask indicating stereo mixer channels. If a bit is set, the corresponding channel is stereo; if it is unset, the channel is either monophonic or not supported by the mixer (use in combination with \method{channels()} to determine which). See the code example for the \method{channels()} function for an example of getting data from a bitmask. \end{methoddesc} \begin{methoddesc}[mixer device]{reccontrols}{} Returns a bitmask specifying the mixer controls that may be used to record. See the code example for \method{controls()} for an example of reading from a bitmask. \end{methoddesc} \begin{methoddesc}[mixer device]{get}{channel} Returns the volume of a given mixer channel. The returned volume is a 2-tuple \code{(left_volume,right_volume)}. Volumes are specified as numbers from 0 (silent) to 100 (full volume). If the channel is monophonic, a 2-tuple is still returned, but both channel volumes are the same. If an unknown channel is specified, \exception{error} is raised. \end{methoddesc} \begin{methoddesc}[mixer device]{set}{channel, (left, right)} Sets the volume for a given mixer channel to \code{(left,right)}. \code{left} and \code{right} must be ints and between 0 (silent) and 100 (full volume). On success, the new volume is returned as a 2-tuple. Note that this may not be exactly the same as the volume specified, because of the limited resolution of some soundcard's mixers. Raises \exception{IOError} if an invalid mixer channel was specified; \exception{TypeError} if the argument format was incorrect, and \exception{error} if the specified volumes were out-of-range. \end{methoddesc} \begin{methoddesc}[mixer device]{get_recsrc}{} This method returns a bitmask indicating which channel or channels are currently being used as a recording source. \end{methoddesc} \begin{methoddesc}[mixer device]{set_recsrc}{bitmask} Call this function to specify a recording source. Returns a bitmask indicating the new recording source (or sources) if successful; raises \exception{IOError} if an invalid source was specified. To set the current recording source to the microphone input: \begin{verbatim} mixer.setrecsrc (1 << ossaudiodev.SOUND_MIXER_MIC) \end{verbatim} \end{methoddesc}