C: Linux C 编程 - SDL音频处理

音频处理

 

采样率

音频格式

 

 

 

 +----------------------sample is signed if set
 |
 |        +----------sample is bigendian if set
 |        |
 |        |           +--sample is float if set
 |        |           |
 |        |           |  +--sample bit size---+
 |        |           |  |                    |
15 14 13 12 11 10  9  8  7  6  5  4  3  2  1  0

各字段解释

sample is signed if set:

对应下面的signed，unsigned。

 

sample is bigendian if set:

对应下面的little-endian byte order，big-endian byte order。

 

sample is float if set:

对应下面的floating point。

 

sample bit size:

有8位，16位，32位的。对应下面的8-bit support，16-bit support，32-bit support。

 

 

8-bit support
AUDIO_S8	signed 8-bit samples
AUDIO_U8	unsigned 8-bit samples
16-bit support
AUDIO_S16LSB	signed 16-bit samples in little-endian byte order
AUDIO_S16MSB	signed 16-bit samples in big-endian byte order
AUDIO_S16SYS	signed 16-bit samples in native byte order
AUDIO_S16	AUDIO_S16LSB
AUDIO_U16LSB	unsigned 16-bit samples in little-endian byte order
AUDIO_U16MSB	unsigned 16-bit samples in big-endian byte order
AUDIO_U16SYS	unsigned 16-bit samples in native byte order
AUDIO_U16	AUDIO_U16LSB
32-bit support (new to SDL 2.0)
AUDIO_S32LSB	32-bit integer samples in little-endian byte order
AUDIO_S32MSB	32-bit integer samples in big-endian byte order
AUDIO_S32SYS	32-bit integer samples in native byte order
AUDIO_S32	AUDIO_S32LSB
float support (new to SDL 2.0)
AUDIO_F32LSB	32-bit floating point samples in little-endian byte order
AUDIO_F32MSB	32-bit floating point samples in big-endian byte order
AUDIO_F32SYS	32-bit floating point samples in native byte order
AUDIO_F32	AUDIO_F32LSB

 

/**

 *  \name Audio format flags

 *

 *  Defaults to LSB byte order.

 */

/* @{ */

#define AUDIO_U8        0x0008  /**< Unsigned 8-bit samples */

#define AUDIO_S8        0x8008  /**< Signed 8-bit samples */

#define AUDIO_U16LSB    0x0010  /**< Unsigned 16-bit samples */

#define AUDIO_S16LSB    0x8010  /**< Signed 16-bit samples */

#define AUDIO_U16MSB    0x1010  /**< As above, but big-endian byte order */

#define AUDIO_S16MSB    0x9010  /**< As above, but big-endian byte order */

#define AUDIO_U16       AUDIO_U16LSB

#define AUDIO_S16       AUDIO_S16LSB

/* @} */

 

/**

 *  \name int32 support

 */

/* @{ */

#define AUDIO_S32LSB    0x8020  /**< 32-bit integer samples */

#define AUDIO_S32MSB    0x9020  /**< As above, but big-endian byte order */

#define AUDIO_S32       AUDIO_S32LSB

/* @} */

 

/**

 *  \name float32 support

 */

/* @{ */

#define AUDIO_F32LSB    0x8120  /**< 32-bit floating point samples */

#define AUDIO_F32MSB    0x9120  /**< As above, but big-endian byte order */

#define AUDIO_F32       AUDIO_F32LSB

/* @} */

 

/**

 *  \name Native audio byte ordering

 */

/* @{ */

#if SDL_BYTEORDER == SDL_LIL_ENDIAN

#define AUDIO_U16SYS    AUDIO_U16LSB

#define AUDIO_S16SYS    AUDIO_S16LSB

#define AUDIO_S32SYS    AUDIO_S32LSB

#define AUDIO_F32SYS    AUDIO_F32LSB

#else

#define AUDIO_U16SYS    AUDIO_U16MSB

#define AUDIO_S16SYS    AUDIO_S16MSB

#define AUDIO_S32SYS    AUDIO_S32MSB

#define AUDIO_F32SYS    AUDIO_F32MSB

#endif

 

通道

 

 

音频播放

写道

/**
* The calculated values in this structure are calculated by SDL_OpenAudio().
*
* For multi-channel audio, the default SDL channel mapping is:
* 2: FL FR (stereo)
* 3: FL FR LFE (2.1 surround)
* 4: FL FR BL BR (quad)
* 5: FL FR FC BL BR (quad + center)
* 6: FL FR FC LFE SL SR (5.1 surround - last two can also be BL BR)
* 7: FL FR FC LFE BC SL SR (6.1 surround)
* 8: FL FR FC LFE BL BR SL SR (7.1 surround)
*/
typedef struct SDL_AudioSpec
{
int freq; /**< DSP frequency -- samples per second */
SDL_AudioFormat format; /**< Audio data format */
Uint8 channels; /**< Number of channels: 1 mono, 2 stereo */
Uint8 silence; /**< Audio buffer silence value (calculated) */
Uint16 samples; /**< Audio buffer size in sample FRAMES (total samples divided by channel count) */
Uint16 padding; /**< Necessary for some compile environments */
Uint32 size; /**< Audio buffer size in bytes (calculated) */
SDL_AudioCallback callback; /**< Callback that feeds the audio device (NULL to use SDL_QueueAudio()). */
void *userdata; /**< Userdata passed to callback (ignored for NULL callbacks). */
} SDL_AudioSpec;

各字段解释：

freq

采样率

format

音频数据格式

channels

通道数

silence

静默

samples

padding

size

音频缓冲区大小

callback

回调函数

 

函数原型

void SDLCALL SDL_AudioCallback(void *userdata, Uint8 * stream, int len);

第1个参数userdata是由用户自定义（application-specific）传递的参数，这个参数由userdata指定；

第2个参数stream表示指向音频数据缓冲区的指针；

第3个参数len表示缓冲区大小（字节数）。

 

userdata

用户自定义（application-specific）传递的数据

 

 

播放wav格式的音频

#include<stdio.h>
#include<SDL_audio.h>

struct sample 
{
  Uint8 *data;
  Uint32 d_pos;
  Uint32 d_len;
} audio;

void sdl_callback(void *unused, Uint8 *stream, int len)
{
  int amount = audio.d_len - audio.d_pos;
  if (amount > len) 
  {
    amount = len;
  }
  if (amount <= 0)
  {
    SDL_PauseAudio(1);
    return;
  }
  SDL_memcpy(stream, audio.data + audio.d_pos, amount);
  audio.d_pos += amount;
}

// mp h:\\sample.wav
// mp h:\\yuganqingwuguan-c_a_wmav2.wav
// mp h:\\yuganqingwuguan.wav
int main(int argc, char **argv)
{
  char *filename;
  SDL_AudioSpec audio_spec;
  
  if (argc != 2)
  {
    fprintf(stderr, "invalid args...\n");
    return 1;
  }

  filename = *(argv + 1);
  if (SDL_LoadWAV(filename, &audio_spec, &audio.data, &audio.d_len) == NULL)
  {
    fprintf(stderr, "load wav err: %s\n", SDL_GetError());
    return 1;
  }

  audio_spec.callback = sdl_callback;
  audio_spec.userdata = NULL;

  if (SDL_OpenAudio(&audio_spec, NULL) < 0)
  {
    fprintf(stderr, "open audio err: %s\n", SDL_GetError());
    return -1;
  }

  SDL_PauseAudio(0);
  printf("playing...%s\n", filename);

  while ((SDL_GetAudioStatus() == SDL_AUDIO_PLAYING)) 
  {
    SDL_Delay(1000);
  }
  printf("played!\n");

  SDL_CloseAudio();
  SDL_FreeWAV(audio.data);
  SDL_Quit();
  return 0;
}

编译

这里一次性完成编译链接。编译的时候注意通过“-I”指定头文件目录，在链接的时候通过“-L”指定要链接的静态库文件目录，以及通过“-l”指定要链接的静态库。

 

gcc -I D:\sbin\usr\local\sdl\include\SDL2 -L D:\sbin\usr\local\sdl\lib sdl_test.c -o sdl_test -lSDL2

 

运行

在运行之前SDL2.dll拷贝到程序目录下：

>cp -rf d:\sbin\usr\local\sdl\bin\SDL2.dll .

 

mp h:\\sample.wav

mp h:\\yuganqingwuguan-c_a_wmav2.wav

mp h:\\yuganqingwuguan.wav

 

 

#include<stdio.h>
#include<SDL_audio.h>
#include<SDL_log.h>

struct sample 
{
  Uint8 *data;
  Uint32 d_pos;
  Uint32 d_len;
} audio;

void sdl_callback(void *unused, Uint8 *stream, int len)
{
  int amount = audio.d_len - audio.d_pos;
  if (amount > len) 
  {
    amount = len;
  }
  printf("audio: len= %u, pos= %u. audio buffer: @%p, len= %d, amount= %d\n", audio.d_len, audio.d_pos, stream, len, amount);
  if (amount <= 0)
  {
    SDL_PauseAudio(1);
    return;
  }
  SDL_memcpy(stream, audio.data + audio.d_pos, amount);
  audio.d_pos += amount;
}

void display_audio_spec(SDL_AudioSpec *audio_spec)
{
  printf("audio: freq...%d\n", audio_spec->freq);
  printf("audio: format...%d\n", audio_spec->format);
  printf("audio: channels...%d\n", audio_spec->channels);
  printf("audio: silence...%d\n", audio_spec->silence);
  printf("audio: samples...%d\n", audio_spec->samples);
  printf("audio: padding...%d\n", audio_spec->padding);
  printf("audio: size...%d\n", audio_spec->size);
  printf("audio: callback...%p\n", audio_spec->callback);
}

// mp h:\\sample.wav
// mp h:\\yuganqingwuguan-c_a_wmav2.wav
// mp h:\\yuganqingwuguan.wav
int main(int argc, char **argv)
{
  char *filename;

  Uint8 *data;
  Uint32 d_len;
  SDL_AudioSpec audio_spec;
  SDL_AudioCVT audio_cvt;
  
  if (argc != 2)
  {
    fprintf(stderr, "invalid args...\n");
    return 1;
  }

  display_audio_spec(&audio_spec);

  filename = *(argv + 1);
  if (SDL_LoadWAV(filename, &audio_spec, &data, &d_len) == NULL)
  {
    fprintf(stderr, "load wav err: %s\n", SDL_GetError());
    return 1;
  }

  display_audio_spec(&audio_spec);

  /*
  if (SDL_BuildAudioCVT(&audio_cvt, audio_spec.format, audio_spec.channels, audio_spec.freq, AUDIO_S16, 1, 22050) < 0)
  {
    SDL_LogError(SDL_LOG_CATEGORY_ERROR, "build audio cvt err: %s\n", SDL_GetError());
    return 1;
  }
  */
  /*
  if (SDL_BuildAudioCVT(&audio_cvt, audio_spec.format, audio_spec.channels, audio_spec.freq, AUDIO_S16, 2, 22050) < 0)
  {
    SDL_LogError(SDL_LOG_CATEGORY_ERROR, "build audio cvt err: %s\n", SDL_GetError());
    return 1;
  }
  */
  /*
  if (SDL_BuildAudioCVT(&audio_cvt, audio_spec.format, audio_spec.channels, audio_spec.freq, audio_spec.format, audio_spec.channels, audio_spec.freq) < 0)
  {
    SDL_LogError(SDL_LOG_CATEGORY_ERROR, "build audio cvt err: %s\n", SDL_GetError());
    return 1;
  }
  */
  /*
  if (SDL_BuildAudioCVT(&audio_cvt, audio_spec.format, audio_spec.channels, audio_spec.freq, AUDIO_S16, audio_spec.channels == 1 ? audio_spec.channels : 2, audio_spec.freq) < 0)
  {
    SDL_LogError(SDL_LOG_CATEGORY_ERROR, "build audio cvt err: %s\n", SDL_GetError());
    return 1;
  }
  //*/
  //*
  if (SDL_BuildAudioCVT(&audio_cvt, audio_spec.format, audio_spec.channels, audio_spec.freq, AUDIO_S16, audio_spec.channels == 1 ? audio_spec.channels : 2, 34100) < 0)
  {
    SDL_LogError(SDL_LOG_CATEGORY_ERROR, "build audio cvt err: %s\n", SDL_GetError());
    fprintf(stderr, "build audio cvt err: %s\n", SDL_GetError());
    return 1;
  }
  //*/
  /*
  if (SDL_BuildAudioCVT(&audio_cvt, audio_spec.format, audio_spec.channels, audio_spec.freq, AUDIO_S16, audio_spec.channels == 1 ? audio_spec.channels : 2, 44100) < 0)
  {
    SDL_LogError(SDL_LOG_CATEGORY_ERROR, "build audio cvt err: %s\n", SDL_GetError());
    fprintf(stderr, "build audio cvt err: %s\n", SDL_GetError());
    return 1;
  }
  //*/
  /*
  if (SDL_BuildAudioCVT(&audio_cvt, audio_spec.format, audio_spec.channels, audio_spec.freq, AUDIO_S16, audio_spec.channels == 1 ? audio_spec.channels : 2, 84100) < 0)
  {
    SDL_LogError(SDL_LOG_CATEGORY_ERROR, "build audio cvt err: %s\n", SDL_GetError());
    fprintf(stderr, "build audio cvt err: %s\n", SDL_GetError());
    return 1;
  }
  //*/
  audio_cvt.len = d_len;
  audio_cvt.buf = (Uint8 *) SDL_malloc(audio_cvt.len * audio_cvt.len_mult);
  memcpy(audio_cvt.buf, data, d_len);
  SDL_ConvertAudio(&audio_cvt);

  SDL_FreeWAV(data);

  SDL_LockAudio();
  audio.data = audio_cvt.buf;
  audio.d_len = audio_cvt.len_cvt;
  audio.d_pos = 0;
  SDL_UnlockAudio();

  // audio_spec.silence = 1; // 这个设置没用, 由SDL_OpenAudio()计算设置。

  audio_spec.callback = sdl_callback;
  audio_spec.userdata = NULL;

  if (SDL_OpenAudio(&audio_spec, NULL) < 0)
  {
    fprintf(stderr, "open audio err: %s\n", SDL_GetError());
    return -1;
  }

  display_audio_spec(&audio_spec);

  SDL_PauseAudio(0);
  printf("playing...%s\n", filename);

  while ((SDL_GetAudioStatus() == SDL_AUDIO_PLAYING)) 
  {
    SDL_Delay(1000);
  }
  printf("played!\n");

  SDL_CloseAudio();
  SDL_FreeWAV(audio.data);
  SDL_Quit();
  return 0;
}

 

 

如果在程序中包含了SDL.h这个头文件：

#include<SDL.h>

编译链接的时候报如下错误：

/usr/lib/gcc/i686-pc-cygwin/4.5.3/../../../libcygwin.a(libcmain.o): In

 function `main':

/usr/src/debug/cygwin-1.7.18-1/winsup/cygwin/lib/libcmain.c:39: undefi

ned reference to `_WinMain@16'

collect2: ld returned 1 exit status

 

需要将入口函数：

int main(int argc, char **argv);

换成：

int APIENTRY WinMain(HINSTANCE hInstance,

                     HINSTANCE hPrevInstance,

                     LPSTR     lpCmdLine,

                     int       nCmdShow);

同时包含windows.h头文件：

#include<windows.h>

这个时候就是个Win32应用程序了。

#include<stdio.h>
#include<stdlib.h>

#include<windows.h>
#include<SDL.h>
#include<SDL_audio.h>

struct sample 
{
  Uint8 *data;
  Uint32 d_pos;
  Uint32 d_len;
} audio;

void sdl_callback(void *unused, Uint8 *stream, int len)
{
  int amount = audio.d_len - audio.d_pos;
  if (amount > len) 
  {
    amount = len;
  }
  printf("audio: len= %u, pos= %u. audio buffer: @%p, len= %d, amount= %d\n", audio.d_len, audio.d_pos, stream, len, amount);
  if (amount <= 0)
  {
    SDL_PauseAudio(1);
    return;
  }
  SDL_memcpy(stream, audio.data + audio.d_pos, amount);
  audio.d_pos += amount;
}

void display_audio_spec(SDL_AudioSpec *audio_spec)
{
  printf("audio: freq...%d\n", audio_spec->freq);
  printf("audio: format...%d\n", audio_spec->format);
  printf("audio: channels...%d\n", audio_spec->channels);
  printf("audio: silence...%d\n", audio_spec->silence);
  printf("audio: samples...%d\n", audio_spec->samples);
  printf("audio: padding...%d\n", audio_spec->padding);
  printf("audio: size...%d\n", audio_spec->size);
  printf("audio: callback...%p\n", audio_spec->callback);
}

// mp h:\\sample.wav
// mp h:\\yuganqingwuguan-c_a_wmav2.wav
// mp h:\\yuganqingwuguan.wav
int APIENTRY WinMain(HINSTANCE hInstance,
                     HINSTANCE hPrevInstance,
                     LPSTR     lpCmdLine,
                     int       nCmdShow)
{
  char *filename;
  SDL_AudioSpec audio_spec;

  display_audio_spec(&audio_spec);

  filename = "h:\\sample.wav"; // *(argv + 1); "h:\\sample.wav";
  if (SDL_LoadWAV(filename, &audio_spec, &audio.data, &audio.d_len) == NULL)
  {
    fprintf(stderr, "load wav err: %s\n", SDL_GetError());
    return 1;
  }
  display_audio_spec(&audio_spec);

  // audio_spec.silence = 1; // 这个设置没用, 由SDL_OpenAudio()计算设置。

  audio_spec.callback = sdl_callback;
  audio_spec.userdata = NULL;

  if (SDL_OpenAudio(&audio_spec, NULL) < 0)
  {
    fprintf(stderr, "open audio err: %s\n", SDL_GetError());
    return -1;
  }

  display_audio_spec(&audio_spec);

  SDL_PauseAudio(0);
  printf("playing...%s\n", filename);

  while ((SDL_GetAudioStatus() == SDL_AUDIO_PLAYING)) 
  {
    SDL_Delay(1000);
  }
  printf("played!\n");

  SDL_CloseAudio();
  SDL_FreeWAV(audio.data);
  SDL_Quit();
  return 0;
}

编译

这里一次性完成编译链接。编译的时候注意通过“-I”指定头文件目录，在链接的时候通过“-L”指定要链接的静态库文件目录，以及通过“-l”指定要链接的静态库。

 

gcc -I D:\sbin\usr\local\sdl\include\SDL2 -L D:\sbin\usr\local\sdl\lib sdl_test_v2.c -o sdl_test_v2 -lSDL2

 

运行

在运行之前SDL2.dll拷贝到程序目录下：

>cp -rf d:\sbin\usr\local\sdl\bin\SDL2.dll .

 

mp

 

SDL2_mixer

 

#include<SDL_events.h>
#include<SDL_mixer.h>

int main(int argc, char** argv)
{
  SDL_Event e;
  int exit = 0;

  Mix_Music *music;

  // frequency
  // 
  // format
  // 
  // channels
  // 
  // chunksize
  // MIX_MAX_VOLUME
  Mix_OpenAudio(MIX_DEFAULT_FREQUENCY, MIX_DEFAULT_FORMAT, MIX_DEFAULT_CHANNELS, 2048); // 这里chunksize参数指定为2048比较正常

  music = Mix_LoadMUS("h:\\yuganqingwuguan.wav"); // h:\\yuganqingwuguan.mp3 // h:\\yuganqingwuguan.wav
  if (music == NULL)
  {
    fprintf(stderr, "load music err: %s\n", SDL_GetError());
    return -1;
  }
  Mix_PlayMusic(music, 1);

  while(! exit)
  {
    while (SDL_PollEvent(&e))
    {
      if (e.type == SDL_QUIT)
      {
        exit = 1;
        
      }
    }
  }
}