audio.h

   1 #ifndef _AUDIO_H
   2 #define _AUDIO_H
   3
   4 #include <libconfig.h>
   5 #include <stdint.h>
   6
   7 // clang-format off
   8 // Play samples provided may be from the source, in which case they will be timed
   9 // or they may be generated by Shairport Sync, in which case they will not be timed.
  10
  11 // Typically these would be samples of silence, which may be dithered, sent during the lead-in to
  12 // the start of the material, or inserted instead of a missing frame, or after a flush.
  13 // clang-format on
  14
  15 typedef enum {
  16   play_samples_are_untimed = 0, // typically the samples are (possibly dithered) silence
  17   play_samples_are_timed,       // timed and numbered.
  18 } play_samples_type;
  19
  20 typedef struct {
  21   double current_volume_dB;
  22   int32_t minimum_volume_dB;
  23   int32_t maximum_volume_dB;
  24 } audio_parameters;
  25
  26 typedef struct {
  27   void (*help)(void);
  28   char *name;
  29
  30   // start of program
  31   int (*init)(int argc, char **argv);
  32   // at end of program
  33   void (*deinit)(void);
  34
  35   int (*prepare)(void); // looks and sets stuff in the config data structure
  36
  37   void (*start)(int sample_rate, int sample_format);
  38
  39   // block of samples
  40   int (*play)(void *buf, int samples, int sample_type, uint32_t timestamp, uint64_t playtime);
  41   void (*stop)(void);
  42
  43   // may be null if no implemented
  44   int (*is_running)(
  45       void); // if implemented, will return 0 if everything is okay, non-zero otherwise
  46
  47   // may be null if not implemented
  48   void (*flush)(void);
  49
  50   // returns the delay before the next frame to be sent to the device would actually be audible.
  51   // almost certainly wrong if the buffer is empty, so put silent buffers into it to make it busy.
  52   // will change dynamically, so keep watching it. Implemented in ALSA only.
  53   // returns a negative error code if there's a problem
  54   int (*delay)(long *the_delay); // snd_pcm_sframes_t is a signed long
  55   int (*stats)(uint64_t *raw_measurement_time, uint64_t *corrected_measurement_time,
  56                uint64_t *delay,
  57                uint64_t *frames_sent_to_dac); // use this to get the true rate of the DAC
  58
  59   // may be NULL, in which case soft volume is applied
  60   void (*volume)(double vol);
  61
  62   // may be NULL, in which case soft volume parameters are used
  63   void (*parameters)(audio_parameters *info);
  64
  65   // may be NULL, in which case software muting is used.
  66   // also, will return a 1 if it is actually using the mute facility, 0 otherwise
  67   int (*mute)(int do_mute);
  68
  69 } audio_output;
  70
  71 audio_output *audio_get_output(const char *name);
  72 void audio_ls_outputs(void);
  73 void parse_general_audio_options(void);
  74
  75 #endif //_AUDIO_H