Android中播放DSD音樂

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Github上有個簡單的Alsa DSD測試程式，可以播放DSD，地址位於：https://github.com/zonque/alsa-dsd-player 細看其代碼，發現有ALSA_FORMAT_SND_PCM_FORMAT_DSD_U8的定義，詳情如下：

#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

那麼在Android中能運行這個測試程式嗎？ALSA_FORMAT_SND_PCM_FORMAT_DSD_U8似乎是亮點，之前沒有看到過。嘗試在Android的源碼中尋找它的定義，沒找到。但是在標準的alsa-lib中找到了：

typedef enum _snd_pcm_format {125  SND_PCM_FORMAT_UNKNOWN = -1,127  SND_PCM_FORMAT_S8 = 0,129  SND_PCM_FORMAT_U8,131  SND_PCM_FORMAT_S16_LE,133  SND_PCM_FORMAT_S16_BE,135  SND_PCM_FORMAT_U16_LE,137  SND_PCM_FORMAT_U16_BE,139  SND_PCM_FORMAT_S24_LE,141  SND_PCM_FORMAT_S24_BE,143  SND_PCM_FORMAT_U24_LE,145  SND_PCM_FORMAT_U24_BE,147  SND_PCM_FORMAT_S32_LE,149  SND_PCM_FORMAT_S32_BE,151  SND_PCM_FORMAT_U32_LE,153  SND_PCM_FORMAT_U32_BE,155  SND_PCM_FORMAT_FLOAT_LE,157  SND_PCM_FORMAT_FLOAT_BE,159  SND_PCM_FORMAT_FLOAT64_LE,161  SND_PCM_FORMAT_FLOAT64_BE,163  SND_PCM_FORMAT_IEC958_SUBFRAME_LE,165  SND_PCM_FORMAT_IEC958_SUBFRAME_BE,167  SND_PCM_FORMAT_MU_LAW,169  SND_PCM_FORMAT_A_LAW,171  SND_PCM_FORMAT_IMA_ADPCM,173  SND_PCM_FORMAT_MPEG,175  SND_PCM_FORMAT_GSM,177  SND_PCM_FORMAT_SPECIAL = 31,179  SND_PCM_FORMAT_S24_3LE = 32,181  SND_PCM_FORMAT_S24_3BE,183  SND_PCM_FORMAT_U24_3LE,185  SND_PCM_FORMAT_U24_3BE,187  SND_PCM_FORMAT_S20_3LE,189  SND_PCM_FORMAT_S20_3BE,191  SND_PCM_FORMAT_U20_3LE,193  SND_PCM_FORMAT_U20_3BE,195  SND_PCM_FORMAT_S18_3LE,197  SND_PCM_FORMAT_S18_3BE,199  SND_PCM_FORMAT_U18_3LE,201  SND_PCM_FORMAT_U18_3BE,202  /* G.723 (ADPCM) 24 kbit/s, 8 samples in 3 bytes */203  SND_PCM_FORMAT_G723_24,204  /* G.723 (ADPCM) 24 kbit/s, 1 sample in 1 byte */205  SND_PCM_FORMAT_G723_24_1B,206  /* G.723 (ADPCM) 40 kbit/s, 8 samples in 3 bytes */207  SND_PCM_FORMAT_G723_40,208  /* G.723 (ADPCM) 40 kbit/s, 1 sample in 1 byte */209  SND_PCM_FORMAT_G723_40_1B,210  /* Direct Stream Digital (DSD) in 1-byte samples (x8) */211  SND_PCM_FORMAT_DSD_U8,212  /* Direct Stream Digital (DSD) in 2-byte samples (x16) */213  SND_PCM_FORMAT_DSD_U16_LE,214  SND_PCM_FORMAT_LAST = SND_PCM_FORMAT_DSD_U16_LE,215 216 #if __BYTE_ORDER == __LITTLE_ENDIAN217 218  SND_PCM_FORMAT_S16 = SND_PCM_FORMAT_S16_LE,220  SND_PCM_FORMAT_U16 = SND_PCM_FORMAT_U16_LE,222  SND_PCM_FORMAT_S24 = SND_PCM_FORMAT_S24_LE,224  SND_PCM_FORMAT_U24 = SND_PCM_FORMAT_U24_LE,226  SND_PCM_FORMAT_S32 = SND_PCM_FORMAT_S32_LE,228  SND_PCM_FORMAT_U32 = SND_PCM_FORMAT_U32_LE,230  SND_PCM_FORMAT_FLOAT = SND_PCM_FORMAT_FLOAT_LE,232  SND_PCM_FORMAT_FLOAT64 = SND_PCM_FORMAT_FLOAT64_LE,234  SND_PCM_FORMAT_IEC958_SUBFRAME = SND_PCM_FORMAT_IEC958_SUBFRAME_LE235 #elif __BYTE_ORDER == __BIG_ENDIAN236 237  SND_PCM_FORMAT_S16 = SND_PCM_FORMAT_S16_BE,239  SND_PCM_FORMAT_U16 = SND_PCM_FORMAT_U16_BE,241  SND_PCM_FORMAT_S24 = SND_PCM_FORMAT_S24_BE,243  SND_PCM_FORMAT_U24 = SND_PCM_FORMAT_U24_BE,245  SND_PCM_FORMAT_S32 = SND_PCM_FORMAT_S32_BE,247  SND_PCM_FORMAT_U32 = SND_PCM_FORMAT_U32_BE,249  SND_PCM_FORMAT_FLOAT = SND_PCM_FORMAT_FLOAT_BE,251  SND_PCM_FORMAT_FLOAT64 = SND_PCM_FORMAT_FLOAT64_BE,253  SND_PCM_FORMAT_IEC958_SUBFRAME = SND_PCM_FORMAT_IEC958_SUBFRAME_BE254 #else255 #error "Unknown endian"256 #endif257 } snd_pcm_format_t;

暫時還不知具體是怎麼工作的，是透傳DSD資料到硬體？還是alsa-lib中先轉換為標準的PCM？ 但在Android的alsa-lib中，確實是沒有SND_PCM_FORMAT_DSD的定義，應該是被精簡掉了。因此只能考慮採用DSD->PCM轉換成24bit 176K後，再按照標準的PCM方式來播放。

Android中播放DSD音樂