Sound

Scenes can play WAV files. The desktop preview plays them in time with the scene, and fastanim render mixes them into mp4 and webm output. GIFs and frame sequences have no sound, and the browser playground doesn’t play audio yet: audio fails there.

Loading

audio(path) loads a WAV file. A relative path is relative to the script’s directory. .duration is the file’s length in seconds.

let voice = audio("narration.wav");
print(voice.duration);

Playing and waiting

sound(a) is an animation that plays all of a. sound(a, start, end) plays only seconds start to end of it. Like any animation, it lasts as long as the clip, so scene.play waits for the audio to finish before the next call.

scene.play(sound(voice));                 // all of it, then carry on
scene.play(sound(voice, 1.5, 4.0));       // seconds 1.5 to 4 of the file

A sound combines with other animations like any other. Played together, the step lasts until the longest one finishes. In a sequence, each part starts when the previous one ends.

let title = scene.add(text("Hello"));
scene.play([write(title), sound(voice, 0.0, 2.5)]);
scene.play(sequence([sound(voice, 0.0, 1.0), fade_out(title)]));

run_time on a sound changes how long play waits. It doesn’t stretch the audio.

Playing in the background

scene.add_sound(a) and scene.add_sound(a, start, end) start a sound without waiting: time doesn’t advance, so the scene carries on while it plays. scene.wait_for_sounds() waits until every sound started so far has finished.

scene.add_sound(audio("music.wav"));
let c = scene.add(circle(1.0));
scene.play(create(c));
scene.wait_for_sounds();                  // until the music ends

A sound still playing when the scene ends is cut off there.

Previewing

The preview plays sounds while the clock runs at normal speed. Pausing, stepping or scrubbing silences them. When playback resumes, each sound picks up from the current time.