buffer-source-slow-resampling-1.html

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<html class="reftest-wait">

<script>

const blockSize = 128;

// The sample rate is a prime number so that the resampler is not expected to

// simplify in/out fractions.

const rate = 44101;

var context = new window.OfflineAudioContext(1, 3 * blockSize, rate);

// Non-zero buffer, so it can't be optimized away.

var buffer = context.createBuffer(1, 128, rate);

buffer.getChannelData(0)[0] = 1.0;

var source = context.createBufferSource();

source.buffer = buffer;

source.loop = true;

// Initialize the resampler with a slow input rate.

// With the current (Mar 2017) implementation, very slow rates give the

// resampler a very large denominator.

source.playbackRate.setValueAtTime(rate / 0x7fffffff, 0.0);

// Change to a moderate input rate.

// With the current implementation, skip_frac_num increases by den_rate for

// each output sample and so one block before the change in playback rate is

// enough for high skip_frac_num at the time of the change.

const changeBlock = 1;

const changeBlockSeconds = changeBlock * blockSize / rate;

// With the current speex_resampler_set_rate_frac() implementation, the

// moderate resampler denominator is still large enough to trigger overflow of

// 32-bit unsigned integer arithmetic.

source.playbackRate.setValueAtTime(rate / (rate + 1), changeBlockSeconds);

source.start(0);

context.startRendering().

  then(function() {

    document.documentElement.removeAttribute("class");

});

</script>