from usbd_audio.h:150
typedef struct
{
uint32_t alt_setting;
uint8_t buffer[AUDIO_TOTAL_BUF_SIZE];
AUDIO_OffsetTypeDef offset;
uint8_t rd_enable;
uint16_t rd_ptr;
uint16_t wr_ptr;
USBD_AUDIO_ControlTypeDef control;
} USBD_AUDIO_HandleTypeDef;