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80 lines
3.9 KiB
HTML
80 lines
3.9 KiB
HTML
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<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="GENERATOR" content="Mozilla/4.77 [en]C-gatewaynet (Win98; U) [Netscape]">
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<meta name="Author" content="Phil Burk">
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<meta name="Description" content="Tutorial for PortAudio, a cross platform, open-source, audio I/O library.It provides a very simple API for recording and/or playing sound using a simple callback function.">
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<meta name="KeyWords" content="audio, tutorial, library, portable, open-source, DirectSound,sound, music, JSyn, synthesis,">
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<title>PortAudio Tutorial</title>
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</head>
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<body>
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<center><table COLS=1 WIDTH="100%" BGCOLOR="#FADA7A" >
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<tr>
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<td>
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<center>
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<h1>
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PortAudio Tutorial</h1></center>
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</td>
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</tr>
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</table></center>
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<h2>
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Blocking Read/Write Functions</h2>
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<blockquote>[Note: These functions are not part of the official PortAudio
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API. They are simply built on top of PortAudio as an extra utility. Also
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note that they are under evaluation and their definition may change.]
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<p>There are two fundamentally different ways to design an audio API. One
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is to use callback functions the way we have already shown. The callback
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function operates under an interrupt or background thread This leaves the
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foreground application free to do other things while the audio just runs
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in the background. But this can sometimes be awkward.
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<p>So we have provided an alternative technique that lets a program generate
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audio in the foreground and then just write it to the audio stream as if
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it was a file. If there is not enough room in the audio buffer for more
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data, then the write function will just block until more room is available.
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This can make it very easy to write an audio example. To use this tool,
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you must add the files "pablio/pablio.c" and "pablio/ringbuffer.c" to your
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project. You must also:
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<blockquote>
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<pre>#include "pablio.h"</pre>
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</blockquote>
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Here is a short excerpt of a program that opens a stream for input and
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output. It then reads a block of samples from input, and writes them to
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output, in a loop. The complete example can be found in "pablio/test_rw.c".
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<blockquote>
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<pre> #define SAMPLES_PER_FRAME (2)
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#define FRAMES_PER_BLOCK (1024)
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SAMPLE samples[SAMPLES_PER_FRAME * FRAMES_PER_BLOCK];
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PaError err;
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PABLIO_Stream *aStream;
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/* Open simplified blocking I/O layer on top of PortAudio. */
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err = OpenAudioStream( &rwbl, SAMPLE_RATE, paFloat32,
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(PABLIO_READ_WRITE | PABLIO_STEREO) );
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if( err != paNoError ) goto error;
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/* Process samples in the foreground. */
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for( i=0; i<(NUM_SECONDS * SAMPLE_RATE); i++ )
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{
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/* Read one block of data into sample array from audio input. */
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ReadAudioStream( aStream, samples, FRAMES_PER_BLOCK );
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/*
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** At this point you could process the data in samples array,
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** and write the result back to the same samples array.
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*/
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/* Write that same frame of data to output. */
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WriteAudioStream( aStream, samples, FRAMES_PER_BLOCK );
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}
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CloseAudioStream( aStream );</pre>
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</blockquote>
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</blockquote>
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<font size=+2><a href="http://www.portaudio.com/">home</a> |
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<a href="pa_tutorial.html">contents</a>
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| <a href="pa_tut_devs.html">previous</a> | <a href="pa_tut_explore.html">next</a></font>
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</body>
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</html>
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