mirror of
https://github.com/cookiengineer/audacity
synced 2025-11-04 16:14:00 +01:00
78 lines
3.7 KiB
HTML
78 lines
3.7 KiB
HTML
<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
|
|
<html>
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
|
|
<meta name="GENERATOR" content="Mozilla/4.75 [en]C-gatewaynet (Win98; U) [Netscape]">
|
|
<meta name="Author" content="Phil Burk">
|
|
<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.">
|
|
<meta name="KeyWords" content="audio, tutorial, library, portable, open-source, DirectSound,sound, music, JSyn, synthesis,">
|
|
<title>PortAudio Tutorial</title>
|
|
</head>
|
|
<body>
|
|
|
|
<center><table COLS=1 WIDTH="100%" BGCOLOR="#FADA7A" >
|
|
<tr>
|
|
<td>
|
|
<center>
|
|
<h1>
|
|
PortAudio Tutorial</h1></center>
|
|
</td>
|
|
</tr>
|
|
</table></center>
|
|
|
|
<h2>
|
|
Blocking Read/Write Functions</h2>
|
|
|
|
<blockquote>[Note: These functions are not part of the official PortAudio
|
|
API. They are simply built on top of PortAudio as an extra utility. Also
|
|
note that they are under evaluation and their definition may change.]
|
|
<p>There are two fundamentally different ways to design an audio API. One
|
|
is to use callback functions the way we have already shown. The callback
|
|
function operates under an interrupt or background thread This leaves the
|
|
foreground application free to do other things while the audio just runs
|
|
in the background. But this can sometimes be awkward.
|
|
<p>So we have provided an alternative technique that lets a program generate
|
|
audio in the foreground and then just write it to the audio stream as if
|
|
it was a file. If there is not enough room in the audio buffer for more
|
|
data, then the write function will just block until more room is available.
|
|
This can make it very easy to write an audio example. To use this tool,
|
|
you must add the files "pablio/pablio.c" and "pablio/ringbuffer.c" to your
|
|
project. You must also:
|
|
<blockquote>
|
|
<pre>#include "pablio.h"</pre>
|
|
</blockquote>
|
|
Here is a short excerpt of a program that opens a stream for input and
|
|
output. It then read a pair of samples at a time from input, and writes
|
|
them to output, in a loop. The complete example can be found in "pablio/test_rw.c".
|
|
<blockquote>
|
|
<pre> SAMPLE samples[2];
|
|
PaError err;
|
|
PABLIO_Stream *aStream;
|
|
|
|
/* Open simplified blocking I/O layer on top of PortAudio. */
|
|
err = OpenAudioStream( &rwbl, SAMPLE_RATE, paFloat32,
|
|
(PABLIO_READ_WRITE | PABLIO_STEREO) );
|
|
if( err != paNoError ) goto error;
|
|
|
|
/* Process samples in the foreground. */
|
|
for( i=0; i<(NUM_SECONDS * SAMPLE_RATE); i++ )
|
|
{
|
|
/* Read one frame of data into sample array from audio input. */
|
|
ReadAudioStream( aStream, samples, 1 );
|
|
/*
|
|
** At this point you could process the data in samples[0] and samples[1],
|
|
** and write the result back to the same samples array.
|
|
*/
|
|
/* Write that same frame of data to output. */
|
|
WriteAudioStream( aStream, samples, 1 );
|
|
}
|
|
|
|
CloseAudioStream( aStream );</pre>
|
|
</blockquote>
|
|
</blockquote>
|
|
<font size=+2><a href="http://www.portaudio.com/">home</a> |
|
|
<a href="pa_tutorial.html">contents</a>
|
|
| <a href="pa_tut_devs.html">previous</a> | <a href="pa_tut_explore.html">next</a></font>
|
|
</body>
|
|
</html>
|