al_get_sample_instance_length - Allegro 5 API

       Return  the  length of the sample instance in sample values.  This property may differ from the length of
       the instance’s sample data.

       al_get_sample_instance_length - Allegro 5 API

al_set_sample_instance_length(3alleg5), al_get_sample_instance_time(3alleg5)

Allegro reference manual                                                  al_get_sample_instance_length(3alleg5)

              #include <allegro5/allegro_audio.h>

              unsigned int al_get_sample_instance_length(const ALLEGRO_SAMPLE_INSTANCE *spl)