I can control volume on iphone or android.
By remove below lines in a2dp sink example.


//esp_avrc_rn_evt_bit_mask_operation(ESP_AVRC_BIT_MASK_OP_SET, &evt_set, ESP_AVRC_RN_VOLUME_CHANGE);
//assert(esp_avrc_tg_set_rn_evt_cap(&evt_set) == ESP_OK);


But I found the analog output will distortion ...