PortAudio阻塞模式
介绍
PortAudio源码包中例子paex_read_write_wire.c的注释。代码：
<![CDATA[#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "portaudio.h"
/* #define SAMPLE_RATE (17932) // Test failure to open with this value. */
#define SAMPLE_RATE (44100) //采样率，每秒采样的次数，采样一次的数据称为一帧
#define FRAMES_PER_BUFFER (1024)//每次阻塞读写需要缓冲的帧数
#define NUM_CHANNELS (2) //单声道or双声道
#define NUM_SECONDS (15) //
/* #define DITHER_FLAG (paDitherOff) */
#define DITHER_FLAG (0) /**/
/* @todo Underflow and overflow is disabled until we fix priming of blocking write. */
#define CHECK_OVERFLOW (0)
#define CHECK_UNDERFLOW (0)
/* Select sample format. *///采样值量化格式即数模转换，paFloat32, paInt32, paInt24, paInt16, paInt8 ...
#if 0
#define PA_SAMPLE_TYPE paFloat32
#define SAMPLE_SIZE (4)
#define SAMPLE_SILENCE (0.0f)
#define CLEAR(a) memset( (a), 0, FRAMES_PER_BUFFER * NUM_CHANNELS * SAMPLE_SIZE )
#define PRINTF_S_FORMAT "%.8f"
#elif 0
#define PA_SAMPLE_TYPE paInt16
#define SAMPLE_SIZE (2)
#define SAMPLE_SILENCE (0)
#define CLEAR(a) memset( (a), 0, FRAMES_PER_BUFFER * NUM_CHANNELS * SAMPLE_SIZE )
#define PRINTF_S_FORMAT "%d"
#elif 1
#define PA_SAMPLE_TYPE paInt24
#define SAMPLE_SIZE (3)
#define SAMPLE_SILENCE (0)
#define CLEAR(a) memset( (a), 0, FRAMES_PER_BUFFER * NUM_CHANNELS * SAMPLE_SIZE )
#define PRINTF_S_FORMAT "%d"
#elif 0
#define PA_SAMPLE_TYPE paInt8
#define SAMPLE_SIZE (1)
#define SAMPLE_SILENCE (0)
#define CLEAR(a) memset( (a), 0, FRAMES_PER_BUFFER * NUM_CHANNELS * SAMPLE_SIZE )
#define PRINTF_S_FORMAT "%d"
#else
#define PA_SAMPLE_TYPE paUInt8
#define SAMPLE_SIZE (1)
#define SAMPLE_SILENCE (128)
#define CLEAR( a ) { \
int i; \
for( i=0; i<FRAMES_PER_BUFFER*NUM_CHANNELS; i++ ) \
((unsigned char *)a)[i] = (SAMPLE_SILENCE); \
}
#define PRINTF_S_FORMAT "%d"
#endif
/*******************************************************************/
int main(void);
int main(void)
{
PaStreamParameters inputParameters, outputParameters;
PaStream *stream = NULL;
PaError err;
char *sampleBlock;
int i;
int numBytes;
printf("patest_read_write_wire.c\n"); fflush(stdout);
//每次阻塞读写缓冲区所占字节数=缓冲的帧数*声道数*量化大小
numBytes = FRAMES_PER_BUFFER * NUM_CHANNELS * SAMPLE_SIZE ;
sampleBlock = (char *) malloc( numBytes ); //开辟缓冲区
if( sampleBlock == NULL )
{
printf("Could not allocate record array.\n");
exit(1);
}
CLEAR( sampleBlock ); //清除缓冲区
err = Pa_Initialize();
if( err != paNoError ) goto error;
inputParameters.device = Pa_GetDefaultInputDevice(); /* default input device */
printf( "Input device # %d.\n", inputParameters.device );
printf( "Input LL: %g s\n", Pa_GetDeviceInfo( inputParameters.device )->defaultLowInputLatency );
printf( "Input HL: %g s\n", Pa_GetDeviceInfo( inputParameters.device )->defaultHighInputLatency );
inputParameters.channelCount = NUM_CHANNELS;
inputParameters.sampleFormat = PA_SAMPLE_TYPE;
inputParameters.suggestedLatency = Pa_GetDeviceInfo( inputParameters.device )->defaultHighInputLatency;
inputParameters.hostApiSpecificStreamInfo = NULL;
outputParameters.device = Pa_GetDefaultOutputDevice(); /* default output device */
printf( "Output device # %d.\n", outputParameters.device );
printf( "Output LL: %g s\n", Pa_GetDeviceInfo( outputParameters.device )->defaultLowOutputLatency );
printf( "Output HL: %g s\n", Pa_GetDeviceInfo( outputParameters.device )->defaultHighOutputLatency );
outputParameters.channelCount = NUM_CHANNELS;
outputParameters.sampleFormat = PA_SAMPLE_TYPE;
outputParameters.suggestedLatency = Pa_GetDeviceInfo(outputParameters.device)->defaultHighOutputLatency;
outputParameters.hostApiSpecificStreamInfo = NULL;
/* -- setup -- */
err = Pa_OpenStream( //打开流
&stream,
&inputParameters, //如果不需要输入流，则为NULL
&outputParameters,
SAMPLE_RATE,
FRAMES_PER_BUFFER,
paClipOff, /* we won't output out of range samples so don't bother clipping them */
NULL, /* no callback, use blocking API */
NULL ); /* no callback, so no callback userData */
if( err != paNoError ) goto error;
err = Pa_StartStream( stream );//启动流，并不是通常意义的开始播放，需要write才能播放
if( err != paNoError ) goto error;
printf("Wire on. Will run %d seconds.\n", NUM_SECONDS); fflush(stdout);
//(NUM_SECONDS*SAMPLE_RATE)/FRAMES_PER_BUFFER即总帧数/每次缓冲的帧数
//也就是需要缓冲的次数
for( i=0; i<(NUM_SECONDS*SAMPLE_RATE)/FRAMES_PER_BUFFER; ++i )
{
//阻塞写入FRAMES_PER_BUFFER帧，注意要与sampleBlock大小匹配
err = Pa_WriteStream( stream, sampleBlock, FRAMES_PER_BUFFER );
if( err && CHECK_UNDERFLOW ) goto xrun;
err = Pa_ReadStream( stream, sampleBlock, FRAMES_PER_BUFFER );
if( err && CHECK_OVERFLOW ) goto xrun;
}
err = Pa_StopStream( stream );//停止流
if( err != paNoError ) goto error;
//清除缓冲区
CLEAR( sampleBlock );
/*
err = Pa_StartStream( stream );
if( err != paNoError ) goto error;
printf("Wire on. Interrupt to stop.\n"); fflush(stdout);
while( 1 )
{
err = Pa_WriteStream( stream, sampleBlock, FRAMES_PER_BUFFER );
if( err ) goto xrun;
err = Pa_ReadStream( stream, sampleBlock, FRAMES_PER_BUFFER );
if( err ) goto xrun;
}
err = Pa_StopStream( stream );
if( err != paNoError ) goto error;
Pa_CloseStream( stream );
*/
free( sampleBlock );//释放缓冲区
//释放流
Pa_Terminate();
return 0;//正确返回
xrun:
if( stream ) {
Pa_AbortStream( stream );
Pa_CloseStream( stream );
}
free( sampleBlock );
Pa_Terminate();
if( err & paInputOverflow )
fprintf( stderr, "Input Overflow.\n" );
if( err & paOutputUnderflow )
fprintf( stderr, "Output Underflow.\n" );
return -2;
error:
if( stream ) {
Pa_AbortStream( stream );
Pa_CloseStream( stream );
}
free( sampleBlock );
Pa_Terminate();
fprintf( stderr, "An error occured while using the portaudio stream\n" );
fprintf( stderr, "Error number: %d\n", err );
fprintf( stderr, "Error message: %s\n", Pa_GetErrorText( err ) );
return -1;
}
]]>
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