sbc.h

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#ifndef __BT_SBC_H__
#define __BT_SBC_H__
 
#include <stdint.h>
 
/* Encode-only SBC for A2DP (Bluetooth Advanced Audio Distribution,
 * Appendix B). Fixed production configuration, matching what every A2DP
 * sink (including Sony ULT WEAR) accepts:
 *   joint stereo, 8 subbands, 16 blocks, Loudness allocation,
 *   44.1 kHz or 48 kHz, configurable bitpool (53 = A2DP high quality).
 *
 * One frame carries 16 blocks x 8 subbands = 128 PCM samples per channel.
 * At bitpool 53 a frame is 119 bytes (~328 kbit/s at 44.1 kHz).
 *
 * Filterbank, Loudness offsets, bit allocation, CRC and packing follow the
 * A2DP spec as implemented by google/libsbc (Apache-2.0); only integer
 * <stdint.h>/<string.h> operations are used so this compiles both in the
 * kernel and in the host unit test. */
#define SBC_NBLOCKS   16
#define SBC_NSUBBANDS 8
#define SBC_NSAMPLES  (SBC_NBLOCKS * SBC_NSUBBANDS)
#define SBC_MAX_FRAME 128
#define SBC_FREQ_44100 0
#define SBC_FREQ_48000 1
 
typedef struct {
    int16_t x[2][SBC_NSUBBANDS][5];
    int32_t y[4];
    int idx;
} BtSbcCh;
 
typedef struct {
    BtSbcCh ch[2];
} BtSbcEnc;
 
void bt_sbc_init(BtSbcEnc* e);
/* Frame length in bytes for a bitpool, or 0 when the bitpool is invalid. */
unsigned bt_sbc_frame_len(int bitpool);
/* Encode 128 interleaved stereo frames (256 int16 samples, LRLR...).
 * freq is SBC_FREQ_44100 or SBC_FREQ_48000. Returns frame bytes in out
 * (SBC_MAX_FRAME available), or -1 on bad parameters. */
int bt_sbc_encode(BtSbcEnc* e, const int16_t* interleaved, int bitpool, int freq,
                  uint8_t* out);
 
#endif