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diff --git a/arch_src/pyalsaaudio-0.2/doc/.svn/text-base/pcm-objects.html.svn-base b/arch_src/pyalsaaudio-0.2/doc/.svn/text-base/pcm-objects.html.svn-base deleted file mode 100644 index 3fc5d78..0000000 --- a/arch_src/pyalsaaudio-0.2/doc/.svn/text-base/pcm-objects.html.svn-base +++ /dev/null @@ -1,331 +0,0 @@ -<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> -<html> -<head> -<link rel="STYLESHEET" href="pyalsaaudio.css" type='text/css' /> -<link rel="first" href="pyalsaaudio.html" title='PyAlsaAudio' /> -<link rel='contents' href='contents.html' title="Contents" /> -<link rel='last' href='about.html' title='About this document...' /> -<link rel='help' href='about.html' title='About this document...' /> -<link rel="next" href="mixer-objects.html" /> -<link rel="prev" href="node7.html" /> -<link rel="parent" href="module-alsaaudio.html" /> -<link rel="next" href="mixer-objects.html" /> -<meta name='aesop' content='information' /> -<title>4.2 PCM Objects</title> -</head> -<body> -<DIV CLASS="navigation"> -<div id='top-navigation-panel' xml:id='top-navigation-panel'> -<table align="center" width="100%" cellpadding="0" cellspacing="2"> -<tr> -<td class='online-navigation'><a rel="prev" title="4.1 PCM Terminology and" - href="node7.html"><img src='previous.png' - border='0' height='32' alt='Previous Page' width='32' /></A></td> -<td class='online-navigation'><a rel="parent" title="4 alsaaudio" - href="module-alsaaudio.html"><img src='up.png' - border='0' height='32' alt='Up One Level' width='32' /></A></td> -<td class='online-navigation'><a rel="next" title="4.3 Mixer Objects" - href="mixer-objects.html"><img src='next.png' - border='0' height='32' alt='Next Page' width='32' /></A></td> -<td align="center" width="100%">PyAlsaAudio</td> -<td class='online-navigation'><a rel="contents" title="Table of Contents" - href="contents.html"><img src='contents.png' - border='0' height='32' alt='Contents' width='32' /></A></td> -<td class='online-navigation'><img src='blank.png' - border='0' height='32' alt='' width='32' /></td> -<td class='online-navigation'><img src='blank.png' - border='0' height='32' alt='' width='32' /></td> -</tr></table> -<div class='online-navigation'> -<b class="navlabel">Previous:</b> -<a class="sectref" rel="prev" href="node7.html">4.1 PCM Terminology and</A> -<b class="navlabel">Up:</b> -<a class="sectref" rel="parent" href="module-alsaaudio.html">4 alsaaudio</A> -<b class="navlabel">Next:</b> -<a class="sectref" rel="next" href="mixer-objects.html">4.3 Mixer Objects</A> -</div> -<hr /></div> -</DIV> -<!--End of Navigation Panel--> - -<H2><A NAME="SECTION002420000000000000000"></A> -<A NAME="pcm-objects"></A> -<BR> -4.2 PCM Objects -</H2> - -<P> -The acronym PCM is short for Pulse Code Modulation and is the method used in ALSA -and many other places to handle playback and capture of sampled sound data. - -<P> -PCM objects in <tt class="module">alsaaudio</tt> are used to do exactly that, either play sample based -sound or capture sound from some input source (perhaps a microphone). The PCM object -constructor takes the following arguments: - -<P> -<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> - <td><nobr><b><span class="typelabel">class</span> <tt id='l2h-6' xml:id='l2h-6' class="class">PCM</tt></b>(</nobr></td> - <td><var></var><big>[</big><var>type</var><big>]</big><var>, </var><big>[</big><var>mode</var><big>]</big><var>, </var><big>[</big><var>cardname</var><big>]</big><var></var>)</td></tr></table></dt> -<dd> - -<P> -<var>type</var> - can be either PCM_CAPTURE or PCM_PLAYBACK (default). - -<P> -<var>mode</var> - can be either PCM_NONBLOCK, PCM_ASYNC, or PCM_NORMAL (the default). -In PCM_NONBLOCK mode, calls to read will return immediately independent of wether -there is any actual data to read. Similarly, write calls will return immediately -without actually writing anything to the playout buffer if the buffer is full. - -<P> -In the current version of <tt class="module">alsaaudio</tt> PCM_ASYNC is useless, since it relies -on a callback procedure, which can't be specified from Python. - -<P> -<var>cardname</var> - specifies which card should be used (this is only relevant -if you have more than one sound card). Omit to use the default sound card - -<P> -This will construct a PCM object with default settings: - -<P> -Sample format: PCM_FORMAT_S16_LE -<BR> -Rate: 8000 Hz -<BR> -Channels: 2 -<BR> -Period size: 32 frames -<BR></dl> - -<P> -PCM objects have the following methods: - -<P> -<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> - <td><nobr><b><tt id='l2h-7' xml:id='l2h-7' class="method">pcmtype</tt></b>(</nobr></td> - <td><var></var>)</td></tr></table></dt> -<dd> -Returns the type of PCM object. Either PCM_CAPTURE or PCM_PLAYBACK. -</dl> - -<P> -<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> - <td><nobr><b><tt id='l2h-8' xml:id='l2h-8' class="method">pcmmode</tt></b>(</nobr></td> - <td><var></var>)</td></tr></table></dt> -<dd> -Return the mode of the PCM object. One of PCM_NONBLOCK, PCM_ASYNC, or PCM_NORMAL -</dl> - -<P> -<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> - <td><nobr><b><tt id='l2h-9' xml:id='l2h-9' class="method">cardname</tt></b>(</nobr></td> - <td><var></var>)</td></tr></table></dt> -<dd> -Return the name of the sound card used by this PCM object. -</dl> - -<P> -<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> - <td><nobr><b><tt id='l2h-10' xml:id='l2h-10' class="method">setchannels</tt></b>(</nobr></td> - <td><var>nchannels</var>)</td></tr></table></dt> -<dd> -Used to set the number of capture or playback channels. Common values are: 1 = mono, 2 = stereo, -and 6 = full 6 channel audio. Few sound cards support more than 2 channels -</dl> - -<P> -<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> - <td><nobr><b><tt id='l2h-11' xml:id='l2h-11' class="method">setrate</tt></b>(</nobr></td> - <td><var>rate</var>)</td></tr></table></dt> -<dd> -Set the sample rate in Hz for the device. Typical values are 8000 (poor sound), 16000, 44100 (cd quality), -and 96000 -</dl> - -<P> -<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> - <td><nobr><b><tt id='l2h-12' xml:id='l2h-12' class="method">setformat</tt></b>(</nobr></td> - <td><var></var>)</td></tr></table></dt> -<dd> -The sound format of the device. Sound format controls how the PCM device interpret data for playback, -and how data is encoded in captures. - -<P> -The following formats are provided by ALSA: -<div class="center"><table class="realtable"> - <thead> - <tr> - <th class="left" >Format</th> - <th class="left" >Description</th> - </tr> - </thead> - <tbody> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_S8</Formats></td> - <td class="left" >Signed 8 bit samples for each channel</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_U8</Formats></td> - <td class="left" >Signed 8 bit samples for each channel</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_S16_LE</Formats></td> - <td class="left" >Signed 16 bit samples for each channel (Little Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_S16_BE</Formats></td> - <td class="left" >Signed 16 bit samples for each channel (Big Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_U16_LE</Formats></td> - <td class="left" >Unsigned 16 bit samples for each channel (Little Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_U16_BE</Formats></td> - <td class="left" >Unsigned 16 bit samples for each channel (Big Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_S24_LE</Formats></td> - <td class="left" >Signed 24 bit samples for each channel (Little Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_S24_BE</Formats></td> - <td class="left" >Signed 24 bit samples for each channel (Big Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_U24_LE</Formats></td> - <td class="left" >Unsigned 24 bit samples for each channel (Little Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_U24_BE</Formats></td> - <td class="left" >Unsigned 24 bit samples for each channel (Big Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_S32_LE</Formats></td> - <td class="left" >Signed 32 bit samples for each channel (Little Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_S32_BE</Formats></td> - <td class="left" >Signed 32 bit samples for each channel (Big Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_U32_LE</Formats></td> - <td class="left" >Unsigned 32 bit samples for each channel (Little Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_U32_BE</Formats></td> - <td class="left" >Unsigned 32 bit samples for each channel (Big Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_FLOAT_LE</Formats></td> - <td class="left" >32 bit samples encoded as float. (Little Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_FLOAT_BE</Formats></td> - <td class="left" >32 bit samples encoded as float (Big Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_FLOAT64_LE</Formats></td> - <td class="left" >64 bit samples encoded as float. (Little Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_FLOAT64_BE</Formats></td> - <td class="left" >64 bit samples encoded as float. (Big Endian byte order)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_MU_LAW</Formats></td> - <td class="left" >A logarithmic encoding (used by Sun .au files)</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_A_LAW</Formats></td> - <td class="left" >Another logarithmic encoding</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_IMA_ADPCM</Formats></td> - <td class="left" >a 4:1 compressed format defined by the Interactive Multimedia Association</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_MPEG</Formats></td> - <td class="left" >MPEG encoded audio?</td></tr> - <tr><td class="left" valign="baseline"><Formats>PCM_FORMAT_GSM</Formats></td> - <td class="left" >9600 constant rate encoding well suitet for speech</td></tr></tbody> -</table></div> - -<P> -</dl> - -<P> -<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> - <td><nobr><b><tt id='l2h-13' xml:id='l2h-13' class="method">setperiodsize</tt></b>(</nobr></td> - <td><var>period</var>)</td></tr></table></dt> -<dd> -Sets the actual period size in frames. Each write should consist of exactly this number of frames, and -each read will return this number of frames (unless the device is in PCM_NONBLOCK mode, in which case -it may return nothing at all) -</dl> - -<P> -<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> - <td><nobr><b><tt id='l2h-14' xml:id='l2h-14' class="method">read</tt></b>(</nobr></td> - <td><var></var>)</td></tr></table></dt> -<dd> -In PCM_NORMAL mode, this function blocks until a full period is available, and then returns a -tuple (length,data) where <em>length</em> is the size in bytes of the captured data, and <em>data</em> -is the captured sound frames as a string. The length of the returned data will be periodsize*framesize -bytes. - -<P> -In PCM_NONBLOCK mode, the call will not block, but will return <code>(0,'')</code> if no new period -has become available since the last call to read. -</dl> - -<P> -<dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> - <td><nobr><b><tt id='l2h-15' xml:id='l2h-15' class="method">write</tt></b>(</nobr></td> - <td><var>data</var>)</td></tr></table></dt> -<dd> -Writes (plays) the sound in data. The length of data <em>must</em> be a multiple of the frame size, and -<em>should</em> be exactly the size of a period. If less than 'period size' frames are provided, the actual -playout will not happen until more data is written. - -<P> -If the device is not in PCM_NONBLOCK mode, this call will block if the kernel buffer is full, and -until enough sound has been played to allow the sound data to be buffered. The call always returns -the size of the data provided - -<P> -In PCM_NONBLOCK mode, the call will return immediately, with a return value of zero, if the buffer is -full. In this case, the data should be written at a later time. - -<P> -</dl> - -<P> -<strong>A few hints on using PCM devices for playback</strong> - -<P> -The most common reason for problems with playback of PCM audio, is that the people don't properly understand -that writes to PCM devices must match <em>exactly</em> the data rate of the device. - -<P> -If too little data is written to the device, it will underrun, and ugly clicking sounds will occur. Conversely, -of too much data is written to the device, the write function will either block (PCM_NORMAL mode) or return zero -(PCM_NONBLOCK mode). - -<P> -If your program does nothing, but play sound, the easiest way is to put the device in PCM_NORMAL mode, and just -write as much data to the device as possible. This strategy can also be achieved by using a separate thread -with the sole task of playing out sound. - -<P> -In GUI programs, however, it may be a better strategy to setup the device, preload the buffer with a few -periods by calling write a couple of times, and then use some timer method to write one period size of data to -the device every period. The purpose of the preloading is to avoid underrun clicks if the used timer -doesn't expire exactly on time. - -<P> -Also note, that most timer API's that you can find for Python will cummulate time delays: If you set the timer -to expire after 1/10'th of a second, the actual timeout will happen slightly later, which will accumulate to -quite a lot after a few seconds. Hint: use time.time() to check how much time has really passed, and add -extra writes as nessecary. - -<P> - -<DIV CLASS="navigation"> -<div class='online-navigation'> -<p></p><hr /> -<table align="center" width="100%" cellpadding="0" cellspacing="2"> -<tr> -<td class='online-navigation'><a rel="prev" title="4.1 PCM Terminology and" - href="node7.html"><img src='previous.png' - border='0' height='32' alt='Previous Page' width='32' /></A></td> -<td class='online-navigation'><a rel="parent" title="4 alsaaudio" - href="module-alsaaudio.html"><img src='up.png' - border='0' height='32' alt='Up One Level' width='32' /></A></td> -<td class='online-navigation'><a rel="next" title="4.3 Mixer Objects" - href="mixer-objects.html"><img src='next.png' - border='0' height='32' alt='Next Page' width='32' /></A></td> -<td align="center" width="100%">PyAlsaAudio</td> -<td class='online-navigation'><a rel="contents" title="Table of Contents" - href="contents.html"><img src='contents.png' - border='0' height='32' alt='Contents' width='32' /></A></td> -<td class='online-navigation'><img src='blank.png' - border='0' height='32' alt='' width='32' /></td> -<td class='online-navigation'><img src='blank.png' - border='0' height='32' alt='' width='32' /></td> -</tr></table> -<div class='online-navigation'> -<b class="navlabel">Previous:</b> -<a class="sectref" rel="prev" href="node7.html">4.1 PCM Terminology and</A> -<b class="navlabel">Up:</b> -<a class="sectref" rel="parent" href="module-alsaaudio.html">4 alsaaudio</A> -<b class="navlabel">Next:</b> -<a class="sectref" rel="next" href="mixer-objects.html">4.3 Mixer Objects</A> -</div> -</div> -<hr /> -<span class="release-info">Release 0.2.</span> -</DIV> -<!--End of Navigation Panel--> - -</BODY> -</HTML> |