Audio Streaming Demo

App: apps/audio_streaming_demo/

Streams synthesized float PCM to the audio device over time (engine PLM-133 / ADR 0042) — the counterpart to a one-shot clip loaded from a file. Each frame the game renders ~1/60 s of a 220 Hz sine tone and tops up the source’s buffer queue; the engine recycles finished buffers and (re)starts playback automatically, so the tone plays continuously. This is the primitive a SoundFont/MIDI synth renders into.

Run from root

% ./plume3d audio_streaming_demo

You should hear a steady 220 Hz sine tone; a small GUI window shows the frequency and the current queued-buffer count.

What it does

• On init, creates a mono 48 kHz streaming source with Audio.newStreamingSource(48000, 1).
• Each update, while fewer than 4 buffers are queued (_src.queuedBuffers < 4), synthesizes 800 float samples (~1/60 s at 48 kHz) of a 0.2-amplitude sine and queues them with _src.queueSamples(list) — interleaved floats in [-1, 1].
• The engine recycles played-out buffers and restarts playback on the initial queue or after an underrun, so keeping a few buffers queued makes the tone gapless.
• Draws a small Gui window showing the frequency and live queuedBuffers count.

Key pattern

import "engine" for Audio

// init: make a source you FEED over time (mono, 48 kHz).
_src = Audio.newStreamingSource(48000, 1)

// update: top the queue up each frame so playback never underruns.
while (_src.queuedBuffers < 4) {
  var samples = []
  for (i in 0...800) {                          // ~1/60 s of audio
    _phase = _phase + 2.0 * Num.pi * 220.0 / 48000
    if (_phase > 2.0 * Num.pi) _phase = _phase - 2.0 * Num.pi
    samples.add(0.2 * _phase.sin)               // float in [-1, 1]
  }
  _src.queueSamples(samples)                    // interleaved for stereo: L,R,L,R…
}

Uses the AL_EXT_FLOAT32 OpenAL path when available, with an int16 fallback. The queue is fed from the main thread, so a stalled frame can underrun — a few buffers of headroom (here 4) absorbs the jitter.

APIs

• Audio — newStreamingSource, queueSamples, queuedBuffers (the streaming section).
• Source — the same foreign object as a file-backed source.
• Gui — the status window.
• Logger — error if the source can’t be created.