Metadata and Notifications

The A2DP Sink can receive information about what is playing on the connected source (e.g. your phone) via AVRC.

Metadata

You can register a callback which is called when the system receives AVRC metadata (esp_avrc_md_attr_mask_t):

void avrc_metadata_callback(uint8_t id, const uint8_t *text) {
  Serial.printf("AVRC metadata rsp: attribute id 0x%x, %s\n", id, text);
}

void setup() {
  Serial.begin(115200);
  a2dp_sink.set_avrc_metadata_callback(avrc_metadata_callback);
  a2dp_sink.start("BT");
}

By default you get the most important information. You can adjust this by calling set_avrc_metadata_attribute_mask() before you start the sink, e.g. if you only need the title and the playing time:

a2dp_sink.set_avrc_metadata_attribute_mask(ESP_AVRC_MD_ATTR_TITLE | ESP_AVRC_MD_ATTR_PLAYING_TIME);

Note that the second parameter of the callback is actually a char* string: even though ESP_AVRC_MD_ATTR_PLAYING_TIME is documented as the media duration in milliseconds, you need to parse it before doing any math on it. See the bt_music_receiver_with_metadata example.

Notifications

Similar to the metadata callback, you can register callbacks for selected AVRC notifications (esp_avrc_rn_param_t):

Method	Provides
set_avrc_rn_playstatus_callback()	the playback status (esp_avrc_playback_stat_t)
set_avrc_rn_play_pos_callback()	the playback position in ms (uint32_t)
set_avrc_rn_track_change_callback()	a track change flag (uint8_t)

See the bt_music_receiver_playing_status_callbacks example.

Connection and Audio State

You can also be notified about changes of the connection state and the audio state with set_on_connection_state_changed() and set_on_audio_state_changed(). See the bt_music_receiver_status_callback example.