LayoutTests/webaudio/audiobuffersource-loop-points.html

<!DOCTYPE html>

<!--
Tests that AudioBufferSourceNode supports loop-points with .loopStart and .loopEnd.
-->

<html>
<head>
<script type="text/javascript" src="resources/audio-testing.js"></script>

</head>
<body>

<script>

window.onload = init;

var sampleRate = 44100.0;
var numberOfNotes = 72; // play over a 6 octave range
var noteDuration = 0.100;
var noteSpacing = noteDuration + 0.005; // leave 5ms of silence between each "note"
var lengthInSeconds = numberOfNotes * noteSpacing;

var context = 0;
var buffer = 0;

function createTestBuffer(frequency, sampleRate) {
    // Create a buffer containing two periods at this frequency.
    // The 1st half is a pure sine wave period scaled by a linear ramp from 0 -> 1.
    // The 2nd half of the buffer corresponds exactly to one pure sine wave period.
    var onePeriodDuration = 1 / frequency;
    var sampleFrameLength = 2 * onePeriodDuration * sampleRate;

    var audioBuffer = context.createBuffer(1, sampleFrameLength, sampleRate);

    var n = audioBuffer.length;
    var channelData = audioBuffer.getChannelData(0);

    for (var i = 0; i < n; ++i) {
        var sample = Math.sin(frequency * 2.0*Math.PI * i / sampleRate);

        // Linear ramp from 0 -> 1 for the first period.
        // Stay at 1 for the 2nd period.
        var scale = i < n / 2 ? i / (n / 2) : 1;
        sample *= scale;

        channelData[i] = sample;
    }

    return audioBuffer;
}

function playNote(time, duration, playbackRate) {
    var source = context.createBufferSource();
    source.buffer = buffer;
    source.playbackRate.value = playbackRate;

    var gainNode = context.createGain();
    source.connect(gainNode);
    gainNode.connect(context.destination);

    // Loop the 2nd half of the buffer.
    // We should be able to hear any problems as glitches if the looping incorrectly indexes to
    // anywhere outside of the desired loop-points, since only the 2nd half is a perfect sine-wave cycle,
    // while the 1st half of the buffer contains a linear ramp of a sine-wave cycle.
    source.loop = true;
    source.loopStart = 0.5 * buffer.duration;
    source.loopEnd = buffer.duration;

    // Play for the given duration.
    source.start(time);
    source.stop(time + duration);

    // Apply a quick linear fade-out to avoid a click at the end of the note.
    gainNode.gain.value = 1;
    gainNode.gain.setValueAtTime(1, time + duration - 0.005);
    gainNode.gain.linearRampToValueAtTime(0, time + duration);
}

function init() {
    if (!window.testRunner)
        return;

    // Create offline audio context.
    context = new webkitOfflineAudioContext(2, sampleRate * lengthInSeconds, sampleRate);

    // Create the test buffer.
    // We'll loop this with the loop-points set for the 2nd half of this buffer.
    buffer = createTestBuffer(440.0, sampleRate);

    // Play all the notes as a chromatic scale.
    for (var i = 0; i < numberOfNotes; ++i) {
        var time = i * noteSpacing;
        var semitone = i - numberOfNotes/2; // start three octaves down

        // Convert from semitone to rate.
        var playbackRate = Math.pow(2, semitone / 12);

        playNote(time, noteDuration, playbackRate);
    }

    context.oncomplete = finishAudioTest;
    context.startRendering();

    testRunner.waitUntilDone();
}

</script>

</body>
</html>