Android中播放DSD音乐

Github上有个简单的Alsa DSD测试程序，可以播放DSD，地址位于：https://github.com/zonque/alsa-dsd-player 细看其代码，发现有ALSA_FORMAT_SND_PCM_FORMAT_DSD_U8的定义，详情如下：

#if 1

/* 8-bit DSD */

#define ALSA_FORMAT SND_PCM_FORMAT_DSD_U8

#define SAMPLE_SIZE (sizeof(uint8_t) * 2)

#define SAMPLE_RATE_DIV 1

#else

/* 16-bit DSD */

#define ALSA_FORMAT SND_PCM_FORMAT_DSD_U16

#define SAMPLE_SIZE (sizeof(uint16_t) * 2)

#define SAMPLE_RATE_DIV 2

#endif

那么在Android中能运行这个测试程序吗？ALSA_FORMAT_SND_PCM_FORMAT_DSD_U8似乎是亮点，之前没有看到过。尝试在Android的源码中寻找它的定义，没找到。但是在标准的alsa-lib中找到了：

typedef enum _snd_pcm_format {

  SND_PCM_FORMAT_UNKNOWN = -,

  SND_PCM_FORMAT_S8 = ,

  SND_PCM_FORMAT_U8,

  SND_PCM_FORMAT_S16_LE,

  SND_PCM_FORMAT_S16_BE,

  SND_PCM_FORMAT_U16_LE,

  SND_PCM_FORMAT_U16_BE,

  SND_PCM_FORMAT_S24_LE,

  SND_PCM_FORMAT_S24_BE,

  SND_PCM_FORMAT_U24_LE,

  SND_PCM_FORMAT_U24_BE,

  SND_PCM_FORMAT_S32_LE,

  SND_PCM_FORMAT_S32_BE,

  SND_PCM_FORMAT_U32_LE,

  SND_PCM_FORMAT_U32_BE,

  SND_PCM_FORMAT_FLOAT_LE,

  SND_PCM_FORMAT_FLOAT_BE,

  SND_PCM_FORMAT_FLOAT64_LE,

  SND_PCM_FORMAT_FLOAT64_BE,

  SND_PCM_FORMAT_IEC958_SUBFRAME_LE,

  SND_PCM_FORMAT_IEC958_SUBFRAME_BE,

  SND_PCM_FORMAT_MU_LAW,

  SND_PCM_FORMAT_A_LAW,

  SND_PCM_FORMAT_IMA_ADPCM,

  SND_PCM_FORMAT_MPEG,

  SND_PCM_FORMAT_GSM,

  SND_PCM_FORMAT_SPECIAL = ,

  SND_PCM_FORMAT_S24_3LE = ,

  SND_PCM_FORMAT_S24_3BE,

  SND_PCM_FORMAT_U24_3LE,

  SND_PCM_FORMAT_U24_3BE,

  SND_PCM_FORMAT_S20_3LE,

  SND_PCM_FORMAT_S20_3BE,

  SND_PCM_FORMAT_U20_3LE,

  SND_PCM_FORMAT_U20_3BE,

  SND_PCM_FORMAT_S18_3LE,

  SND_PCM_FORMAT_S18_3BE,

  SND_PCM_FORMAT_U18_3LE,

  SND_PCM_FORMAT_U18_3BE,

  /* G.723 (ADPCM) 24 kbit/s, 8 samples in 3 bytes */

  SND_PCM_FORMAT_G723_24,

  /* G.723 (ADPCM) 24 kbit/s, 1 sample in 1 byte */

  SND_PCM_FORMAT_G723_24_1B,

  /* G.723 (ADPCM) 40 kbit/s, 8 samples in 3 bytes */

  SND_PCM_FORMAT_G723_40,

  /* G.723 (ADPCM) 40 kbit/s, 1 sample in 1 byte */

  SND_PCM_FORMAT_G723_40_1B,

  /* Direct Stream Digital (DSD) in 1-byte samples (x8) */

  SND_PCM_FORMAT_DSD_U8,

  /* Direct Stream Digital (DSD) in 2-byte samples (x16) */

  SND_PCM_FORMAT_DSD_U16_LE,

  SND_PCM_FORMAT_LAST = SND_PCM_FORMAT_DSD_U16_LE,

 #if __BYTE_ORDER == __LITTLE_ENDIAN

  SND_PCM_FORMAT_S16 = SND_PCM_FORMAT_S16_LE,

  SND_PCM_FORMAT_U16 = SND_PCM_FORMAT_U16_LE,

  SND_PCM_FORMAT_S24 = SND_PCM_FORMAT_S24_LE,

  SND_PCM_FORMAT_U24 = SND_PCM_FORMAT_U24_LE,

  SND_PCM_FORMAT_S32 = SND_PCM_FORMAT_S32_LE,

  SND_PCM_FORMAT_U32 = SND_PCM_FORMAT_U32_LE,

  SND_PCM_FORMAT_FLOAT = SND_PCM_FORMAT_FLOAT_LE,

  SND_PCM_FORMAT_FLOAT64 = SND_PCM_FORMAT_FLOAT64_LE,

  SND_PCM_FORMAT_IEC958_SUBFRAME = SND_PCM_FORMAT_IEC958_SUBFRAME_LE

 #elif __BYTE_ORDER == __BIG_ENDIAN

  SND_PCM_FORMAT_S16 = SND_PCM_FORMAT_S16_BE,

  SND_PCM_FORMAT_U16 = SND_PCM_FORMAT_U16_BE,

  SND_PCM_FORMAT_S24 = SND_PCM_FORMAT_S24_BE,

  SND_PCM_FORMAT_U24 = SND_PCM_FORMAT_U24_BE,

  SND_PCM_FORMAT_S32 = SND_PCM_FORMAT_S32_BE,

  SND_PCM_FORMAT_U32 = SND_PCM_FORMAT_U32_BE,

  SND_PCM_FORMAT_FLOAT = SND_PCM_FORMAT_FLOAT_BE,

  SND_PCM_FORMAT_FLOAT64 = SND_PCM_FORMAT_FLOAT64_BE,

  SND_PCM_FORMAT_IEC958_SUBFRAME = SND_PCM_FORMAT_IEC958_SUBFRAME_BE

 #else

 #error "Unknown endian"

 #endif

 } snd_pcm_format_t;

暂时还不知具体是怎么工作的，是透传DSD数据到硬件？还是alsa-lib中先转换为标准的PCM？但在Android的alsa-lib中，确实是没有SND_PCM_FORMAT_DSD的定义，应该是被精简掉了。因此只能考虑采用DSD->PCM转换成24bit 176K后，再按照标准的PCM方式来播放。

巴特西

Android中播放DSD音乐

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