al_set_audio_stream_speed - Allegro 5 API

       Set the relative playback speed of the stream.  1.0 means normal speed.

       Return true on success, false on failure.  Will fail if the audio stream is attached directly to a voice.

       al_set_audio_stream_speed - Allegro 5 API

al_get_audio_stream_speed(3alleg5).

Allegro reference manual                                                      al_set_audio_stream_speed(3alleg5)

              #include <allegro5/allegro_audio.h>

              bool al_set_audio_stream_speed(ALLEGRO_AUDIO_STREAM *stream, float val)