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 {
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_ENDIAN
217
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_LE
235 #elif __BYTE_ORDER == __BIG_ENDIAN
236
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_BE
254 #else
255 #error "Unknown endian"
256 #endif
257 } 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。