Question

我正在尝试使用nodejs库https://github.com/duobeiyun/node-sdl-speaker在特定声卡的特定音频通道上播放声音，但是我的问题并不特定于该库。这是一个SDL音频问题。

通过修改src/SDLSpeaker.cpp，我可以使用SDL_OpenAudioDevice而不是SDL_OpenAudio选择声音设备。我用以下代码替换第62行：

// Select second audio device
if (int errorCode = SDL_OpenAudioDevice(SDL_GetAudioDeviceName(1, 0), 0, &wanted_spec, NULL, SDL_AUDIO_ALLOW_FORMAT_CHANGE) < 0) {
[…]

现在，我想仅将声音输出强制为“左”。我认为我应该通过更改fill_audio来做到这一点，但是我不知道该怎么做...：（

Answer 1

我找到了解决方案！ SDL不适合我的需要，SDL_MIXER很适合！

我正在基于编写的C代码编写节点插件：

#include <SDL2/SDL.h>
#include <SDL2/SDL_mixer.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
  int continuer = 1;
  SDL_Init(SDL_INIT_AUDIO);
  Mix_Init(MIX_INIT_MP3);

  int i, count = SDL_GetNumAudioDevices(0);

  printf("-----------------------------------------\n");
  printf("Available audio devices:\n");
  for (i = 0; i < count; ++i)
  {
    printf("    - Audio device %d: %s\n", i, SDL_GetAudioDeviceName(i, 0));
  }
  printf("\n");

  if (argc <= 2)
  {
    return EXIT_FAILURE;
  }

  char *deviceName = argv[1];

  if (Mix_OpenAudioDevice(44100, MIX_DEFAULT_FORMAT, MIX_DEFAULT_CHANNELS, 1024,
                          deviceName, SDL_AUDIO_ALLOW_ANY_CHANGE) == -1)
  {
    printf("[SDL ERROR] :: %s\n\n", Mix_GetError());
    return EXIT_FAILURE;
  }

  printf("Audio device \"%s\" opened with success\n", deviceName);
  printf("-----------------------------------------\n\n");

  int MAX_SOUNDS = argc - 3;
  int currentSound = 0;
  char **files; // = {"file1.wav", "ding.wav"};

  files = (char **)malloc(MAX_SOUNDS * sizeof(char *));

  for (int i = 0; i < MAX_SOUNDS; ++i)
  {
    files[i] = argv[3 + i];
  }

  Mix_AllocateChannels(1);

  if (!Mix_SetPanning(0, argv[2][0] == '1' ? 255 : 0,
                      argv[2][0] == '1' ? 0 : 255))
  {
    printf("[SDL ERROR] :: Mix_SetPanning: %s\n", Mix_GetError());
  }

  Mix_Chunk *sounds[MAX_SOUNDS];

  for (int i = 0; i < MAX_SOUNDS; ++i)
  {
    sounds[i] = Mix_LoadWAV(files[i]);
    Mix_VolumeChunk(sounds[i], MIX_MAX_VOLUME);
  }

  Mix_PlayChannel(0, sounds[0], 0);
  bool playing = true;

  while (playing)
  {
    SDL_WaitEvent(NULL);
    playing = Mix_Playing(0) != 0;

    if (!playing && currentSound < MAX_SOUNDS)
    {
      ++currentSound;
      playing = true;

      if (!Mix_SetPanning(0, argv[2][0] == '1' ? 255 : 0,
                          argv[2][0] == '1' ? 0 : 255))
      {
        printf("[SDL ERROR] :: Mix_SetPanning: %s\n", Mix_GetError());
      }

      Mix_PlayChannel(0, sounds[currentSound], 0);
    }

    printf("Channel 0: %s\r", playing ? "PLAYING" : "STOPPED");
  }

  for (int i = 0; i < MAX_SOUNDS; ++i)
  {
    Mix_FreeChunk(sounds[i]);
  }

  Mix_CloseAudio(); // Fermeture de l'API

  printf("\n");

  return EXIT_SUCCESS;
}

在UNIX上，要进行编译（必须在系统上安装SDL2和SDL2_Mixer dev依赖项）：

$ cc test-sdl-mixer.cc `sdl2-config --cflags --libs` -lsdl2_mixer

编译后，该应用将在特定声卡的特定通道（仅向左或向右）上顺序播放声音文件。

$ ./a.out "Built-in Output" 1 chime.wav advert.wav

效果很好，但是在我编写的节点模块中，我必须使用child_process fork()才能在2个不同的通道或设备上播放2种声音，因为SDL2和SDL2_Mixer都不会创建播放器/调音台。

节点模块即将上市。

SDL2音频选择输出“通道”

1 个答案: