我正在尝试在 Qt 的 C 代码中使用 alsa 库调用在 RHEL6 中播放波形文件。我正在读取缓冲区（wave_buffer）中的波形文件（“t15.wav”）。由于 alsa 库需要播放原始 PCM 样本，因此已去除波头。此外，我还使用 'snd_pcm_hw_params(PCM, params)' & 'snd_pcm_sw_params_current(PCM, swparams)' 和许多其他调用设置了 PCM 硬件和软件参数。我正在使用“snd_pcm_writei”命令在 PCM 句柄上编写 PCM 样本。为此，我正在从 wave_buffer 读取数据块（32 或 1024 或 2048 或 4096 或 8192 字节），并使用 snd_pcm_writei 命令将其发送以进行播放。如果我选择一小块音频质量会下降，但播放不会中断。如果我使用更大的块（大于 4096 即 8192）我获得了完美的音频质量，但它被中断（当播放需要下一个数据块时）。我的限制是我只能访问块中的数据，而不是文件或整个缓冲区。任何人都可以帮助我消除播放波形数据的中断，以便我可以不间断地播放音频。以下是我的代码： 两个变量 buffer_time 和 period_time 返回周期大小，即块的大小。if buffer_time = 5000 & period_time=1000 alsa 库返回的 period_size 为 32 字节 //音频质量下降但没有中断 如果 buffer_time = 500000 & period_time=100000 alsa 库返回的 period_size 为 8192 字节 //音频质量好但中断了 Tuning这些参数似乎没用，因为我在这方面浪费了很多时间。
波形文件结构：采样率：44100 位/采样：16 通道：2
mainwindow.h----
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <alsa/asoundlib.h>
#define BLOCKSIZE 44100 * 2 * 2 // Sample Rate * Channels * Byte per Sample(Bits per sample / 8)
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
int init_alsa();
int play_snd();
~MainWindow();
snd_pcm_t *PCM;
snd_pcm_sframes_t delayp;
snd_pcm_sframes_t availp;
snd_pcm_sw_params_t *swparams;
snd_pcm_hw_params_t *params;
static snd_pcm_sframes_t period_size;
static snd_pcm_sframes_t buffer_size;
unsigned char wave_buffer[900000];
unsigned char play_buffer[BLOCKSIZE];
int filesize;
FILE *fp;
private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H
mainwindow.cpp---
#include "mainwindow.h"
#include "ui_mainwindow.h"
snd_pcm_sframes_t MainWindow::period_size;
snd_pcm_sframes_t MainWindow::buffer_size;
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
if((fp = fopen("t15.wav","rb"))==NULL)
printf("Error Opening File");
fseek(fp,0L,SEEK_END);
filesize = ftell(fp)-44;
fseek(fp,0L,SEEK_SET);
fseek(fp,44,SEEK_SET);
fread(wave_buffer,filesize,1,fp);
fclose(fp);
delayp = 0;
init_alsa();
play_snd();
}
MainWindow::~MainWindow()
{
delete ui;
}
int MainWindow::init_alsa()
{
unsigned int rate = 44100;
int err,dir;
unsigned int rrate = 44100;
snd_pcm_uframes_t size;
static unsigned int buffer_time = 500000;
static unsigned int period_time = 100000;
static int period_event = 0;
if ((err=snd_pcm_open(&PCM,"plughw:0,0",SND_PCM_STREAM_PLAYBACK, 0)) < 0)
{
fprintf(stderr, "Can't use sound: %s\n", snd_strerror(err));
return err;
}
snd_pcm_hw_params_alloca(¶ms);
snd_pcm_sw_params_alloca(&swparams);
//snd_pcm_nonblock(PCM,0);
/* choose all parameters */
err = snd_pcm_hw_params_any(PCM, params);
if (err < 0) {
printf("Broken configuration for playback: no configurations available: %s\n", snd_strerror(err));
return err;
}
/* set hardware resampling */
err = snd_pcm_hw_params_set_rate_resample(PCM, params, 1);
if (err < 0) {
printf("Resampling setup failed for playback: %s\n", snd_strerror(err));
return err;
}
/* set the interleaved read/write format */
err = snd_pcm_hw_params_set_access(PCM, params, SND_PCM_ACCESS_RW_INTERLEAVED);
if (err < 0) {
printf("Access type not available for playback: %s\n", snd_strerror(err));
return err;
}
/* set the sample format */
err = snd_pcm_hw_params_set_format(PCM, params, SND_PCM_FORMAT_S16_LE);
if (err < 0) {
printf("Sample format not available for playback: %s\n", snd_strerror(err));
return err;
}
/* set the count of channels */
err = snd_pcm_hw_params_set_channels(PCM, params, 2);
if (err < 0) {
printf("Channels count (%i) not available for playbacks: %s\n", 2, snd_strerror(err));
return err;
}
/* set the stream rate */
rrate = rate;
err = snd_pcm_hw_params_set_rate_near(PCM, params, &rrate, 0);
if (err < 0) {
printf("Rate %iHz not available for playback: %s\n", 44100, snd_strerror(err));
return err;
}
if (rrate != 44100) {
printf("Rate doesn't match (requested %iHz, get %iHz)\n", rrate, err);
return -EINVAL;
}
/* set the buffer time */
err = snd_pcm_hw_params_set_buffer_time_near(PCM, params, &buffer_time, &dir);
if (err < 0) {
printf("Unable to set buffer time %i for playback: %s\n", buffer_time, snd_strerror(err));
return err;
}
err = snd_pcm_hw_params_get_buffer_size(params, &size);
if (err < 0) {
printf("Unable to get buffer size for playback: %s\n", snd_strerror(err));
return err;
}
buffer_size = size;
/* set the period time */
err = snd_pcm_hw_params_set_period_time_near(PCM, params, &period_time, &dir);
if (err < 0) {
printf("Unable to set period time %i for playback: %s\n", period_time, snd_strerror(err));
return err;
}
err = snd_pcm_hw_params_get_period_size(params, &size, &dir);
if (err < 0) {
printf("Unable to get period size for playback: %s\n", snd_strerror(err));
return err;
}
period_size = size;
/* write the parameters to device */
err = snd_pcm_hw_params(PCM, params);
if (err < 0) {
printf("Unable to set hw params for playback: %s\n", snd_strerror(err));
return err;
}
printf("Size = %ld",period_size);
snd_pcm_sw_params_current(PCM, swparams); /* get the current swparams */
/* start the transfer when the buffer is almost full: */
/* (buffer_size / avail_min) * avail_min */
snd_pcm_sw_params_set_start_threshold(PCM, swparams, (buffer_size / period_size) * period_size);
/* allow the transfer when at least period_size samples can be processed */
/* or disable this mechanism when period event is enabled (aka interrupt like style processing) */
snd_pcm_sw_params_set_avail_min(PCM, swparams, period_event ? buffer_size : period_size);
snd_pcm_sw_params(PCM, swparams);/* write the parameters to the playback device */
return 1;
}
int MainWindow::play_snd()
{
int curr_pos = 0;
int buff_size = 0;
long val = 0;
while(curr_pos < filesize)
{
if(filesize-curr_pos >= period_size)
{
memcpy(play_buffer,wave_buffer+curr_pos,period_size);
buff_size = period_size;
curr_pos += buff_size;
}
else
{
memcpy(play_buffer,wave_buffer+curr_pos,filesize-curr_pos);
buff_size = filesize - curr_pos;
curr_pos += buff_size;
}
int i=1;
unsigned char *ptr = play_buffer;
while(buff_size > 0)
{
val = snd_pcm_writei(PCM,&play_buffer,buff_size);
if (val == -EAGAIN)
continue;
ptr += val * 2;
buff_size -= val;
}
}
return 0;
}
我有一个类似的 alsa 库的 C 代码，它在运行时生成正弦波样本并使用相同的 snd_pcm_writei 命令播放它们，它可以完美播放而没有任何中断......这是 alsa 库代码---
/*
* This small demo sends a simple sinusoidal wave to your speakers.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sched.h>
#include <errno.h>
#include <getopt.h>
#include "alsa/asoundlib.h"
#include <sys/time.h>
#include <math.h>
static char *device = "plughw:0,0"; /* playback device */
static snd_pcm_format_t format = SND_PCM_FORMAT_S16_LE; /* sample format */
static unsigned int rate = 44100; /* stream rate */
static unsigned int channels = 2; /* count of channels */
static unsigned int buffer_time = 5000; /* ring buffer length in us */
static unsigned int period_time = 1000; /* period time in us */
static double freq = 440; /* sinusoidal wave frequency in Hz */
static int resample = 1; /* enable alsa-lib resampling */
static int period_event = 0; /* produce poll event after each period */
static snd_pcm_sframes_t buffer_size;
static snd_pcm_sframes_t period_size;
static snd_output_t *output = NULL;
snd_pcm_sframes_t delayp;
snd_pcm_sframes_t availp;
static void generate_sine(const snd_pcm_channel_area_t *areas,
snd_pcm_uframes_t offset,
int count, double *_phase)
{
static double max_phase = 2. * M_PI;
double phase = *_phase;
double step = max_phase*freq/(double)rate;
unsigned char *samples[channels];
int steps[channels];
unsigned int chn;
int format_bits = snd_pcm_format_width(format);
unsigned int maxval = (1 << (format_bits - 1)) - 1;
int bps = format_bits / 8; /* bytes per sample */
int phys_bps = snd_pcm_format_physical_width(format) / 8;
int big_endian = snd_pcm_format_big_endian(format) == 1;
int to_unsigned = snd_pcm_format_unsigned(format) == 1;
int is_float = (format == SND_PCM_FORMAT_FLOAT_LE ||
format == SND_PCM_FORMAT_FLOAT_BE);
/* verify and prepare the contents of areas */
for (chn = 0; chn < channels; chn++) {
samples[chn] = /*(signed short *)*/(((unsigned char *)areas[chn].addr) + (areas[chn].first / 8));
steps[chn] = areas[chn].step / 8;
samples[chn] += offset * steps[chn];
}
/* fill the channel areas */
while (count-- > 0) {
union {
float f;
int i;
} fval;
int res, i;
if (is_float)
{
fval.f = sin(phase) * maxval;
res = fval.i;
}
else
res = sin(phase) * maxval;
if (to_unsigned)
res ^= 1U << (format_bits - 1);
for (chn = 0; chn < channels; chn++) {
/* Generate data in native endian format */
if (big_endian) {
for (i = 0; i < bps; i++)
*(samples[chn] + phys_bps - 1 - i) = (res >> i * 8) & 0xff;
} else {
for (i = 0; i < bps; i++)
*(samples[chn] + i) = (res >> i * 8) & 0xff;
}
samples[chn] += steps[chn];
}
phase += step;
if (phase >= max_phase)
phase -= max_phase;
}
*_phase = phase;
}
static int set_hwparams(snd_pcm_t *handle, snd_pcm_hw_params_t *params, snd_pcm_access_t access)
{
unsigned int rrate;
snd_pcm_uframes_t size;
int dir;
snd_pcm_hw_params_any(handle, params); /* choose all parameters */
snd_pcm_hw_params_set_rate_resample(handle, params, resample);/* set hardware resampling */
snd_pcm_hw_params_set_access(handle, params, access); /* set the interleaved read/write format */
snd_pcm_hw_params_set_format(handle, params, format); /* set the sample format */
snd_pcm_hw_params_set_channels(handle, params, channels); /* set the count of channels */
rrate = rate; /* set the stream rate */
snd_pcm_hw_params_set_rate_near(handle, params, &rrate, 0);
snd_pcm_hw_params_set_buffer_time_near(handle, params, &buffer_time, &dir);/* set the buffer time */
snd_pcm_hw_params_get_buffer_size(params, &size);
buffer_size = size;
snd_pcm_hw_params_set_period_time_near(handle, params, &period_time, &dir);/* set the period time */
snd_pcm_hw_params_get_period_size(params, &size, &dir);
period_size = size;
snd_pcm_hw_params(handle, params); /* write the parameters to device */
return 0;
}
static int set_swparams(snd_pcm_t *handle, snd_pcm_sw_params_t *swparams)
{
snd_pcm_sw_params_current(handle, swparams); /* get the current swparams */
/* start the transfer when the buffer is almost full: */
/* (buffer_size / avail_min) * avail_min */
snd_pcm_sw_params_set_start_threshold(handle, swparams, (buffer_size / period_size) * period_size);
/* allow the transfer when at least period_size samples can be processed */
/* or disable this mechanism when period event is enabled (aka interrupt like style processing) */
snd_pcm_sw_params_set_avail_min(handle, swparams, period_event ? buffer_size : period_size);
snd_pcm_sw_params(handle, swparams);/* write the parameters to the playback device */
return 0;
}
/*
* Transfer method - write only
*/
static int write_loop(snd_pcm_t *handle, signed short *samples, snd_pcm_channel_area_t *areas)
{
double phase = 0;
signed short *ptr;
int err, cptr;
int i=0;
printf("Period Size = %ld",period_size);
while (1) {
fflush(stdout);
generate_sine(areas, 0, period_size, &phase);
ptr = samples;
cptr = period_size;
i=1;
while (cptr > 0) {
err = snd_pcm_writei(handle, ptr, cptr);
snd_pcm_avail_delay(handle,&availp,&delayp);
printf("available frames =%ld delay = %ld i = %d\n",availp,delayp,i);
if (err == -EAGAIN)
continue;
ptr += err * channels;
cptr -= err;
i++;
}
}
}
/*
* Transfer method - asynchronous notification
*/
int main()
{
snd_pcm_t *handle;
snd_pcm_hw_params_t *hwparams;
snd_pcm_sw_params_t *swparams;
signed short *samples;
unsigned int chn;
snd_pcm_channel_area_t *areas;
snd_pcm_hw_params_alloca(&hwparams);
snd_pcm_sw_params_alloca(&swparams);
snd_output_stdio_attach(&output, stdout, 0);
printf("Playback device is %s\n", device);
printf("Stream parameters are %iHz, %s, %i channels\n", rate, snd_pcm_format_name(format), channels);
printf("Sine wave rate is %.4fHz\n", freq);
snd_pcm_open(&handle, device, SND_PCM_STREAM_PLAYBACK, 0);
set_hwparams(handle, hwparams, SND_PCM_ACCESS_RW_INTERLEAVED);
set_swparams(handle, swparams);
samples = malloc((period_size * channels * snd_pcm_format_physical_width(format)) / 8);
areas = calloc(channels, sizeof(snd_pcm_channel_area_t));
for (chn = 0; chn < channels; chn++) {
areas[chn].addr = samples;
areas[chn].first = chn * snd_pcm_format_physical_width(format);
areas[chn].step = channels * snd_pcm_format_physical_width(format);
}
write_loop(handle, samples, areas);
free(areas);
free(samples);
snd_pcm_close(handle);
return 0;
}