al_set_audio_stream_loop_secs - Allegro 5 API

       Sets  the  loop  points  for the stream in seconds.  Currently this can only be called on streams created
       with  al_load_audio_stream(3alleg5),  al_play_audio_stream(3alleg5),  al_load_audio_stream_f(3alleg5)  or
       al_play_audio_stream_f(3alleg5).

Allegro reference manual                                                  al_set_audio_stream_loop_secs(3alleg5)

       al_set_audio_stream_loop_secs - Allegro 5 API

              #include <allegro5/allegro_audio.h>

              bool al_set_audio_stream_loop_secs(ALLEGRO_AUDIO_STREAM *stream,
                 double start, double end)