voice_set_playmode man page
voice_set_playmode — Adjusts the loop status of the specified voice. Allegro game programming library.
void voice_set_playmode(int voice, int playmode);
Adjusts the loop status of the specified voice. This can be done while the voice is playing, so you can start a sample in looped mode (having set the loop start and end positions to the appropriate values), and then clear the loop flag when you want to end the sound, which will cause it to continue past the loop end, play the subsequent part of the sample, and finish in the normal way. The mode parameter is a bitfield containing the following values:
Plays the sample a single time. This is the default if you don't set the loop flag.
Loops repeatedly through the sample, jumping back to the loop start position upon reaching the loop end.
Plays the sample from beginning to end. This is the default if you don't set the backward flag.
Reverses the direction of the sample. If you combine this with the loop flag, the sample jumps to the loop end position upon reaching the loop start (ie. you do not need to reverse the loop start and end values when you play the sample in reverse).
When used in combination with the loop flag, causes the sample to change direction each time it reaches one of the loop points, so it alternates between playing forwards and in reverse.