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+<!DOCTYPE html>
+<title>Test that DelayNode output channelCount matches that of the delayed input</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+// See https://github.com/WebAudio/web-audio-api/issues/25
+
+// sampleRate is a power of two so that delay times are exact in base-2
+// floating point arithmetic.
+const SAMPLE_RATE = 32768;
+// Arbitrary delay time in frames (but this is assumed a multiple of block
+// size below):
+const DELAY_FRAMES = 3 * 128;
+// Implementations may apply interpolation to input samples, which can spread
+// the effect of input with larger channel counts over neighbouring blocks.
+// This test ignores enough neighbouring blocks to ignore the effects of
+// filter radius of up to this number of frames:
+const INTERPOLATION_GRACE = 128;
+// Number of frames of DelayNode output that are known to be stereo:
+const STEREO_FRAMES = 128;
+// The delay will be increased at this frame to switch DelayNode output back
+// to mono.
+const MONO_OUTPUT_START_FRAME =
+ DELAY_FRAMES + INTERPOLATION_GRACE + STEREO_FRAMES;
+// Number of frames of output that are known to be mono after the known stereo
+// and interpolation grace.
+const MONO_FRAMES = 128;
+// Total length allows for interpolation after effects of stereo input are
+// finished and one block to test return to mono output:
+const TOTAL_LENGTH =
+ MONO_OUTPUT_START_FRAME + INTERPOLATION_GRACE + MONO_FRAMES;
+// maxDelayTime, is a multiple of block size, because the Gecko implementation
+// once had a bug with delayTime = maxDelayTime in this situation:
+const MAX_DELAY_FRAMES = TOTAL_LENGTH + INTERPOLATION_GRACE;
+
+promise_test(() => {
+ let context = new OfflineAudioContext({numberOfChannels: 1,
+ length: TOTAL_LENGTH,
+ sampleRate: SAMPLE_RATE});
+
+ // Only channel 1 of the splitter is connected to the destination.
+ let splitter = new ChannelSplitterNode(context, {numberOfOutputs: 2});
+ splitter.connect(context.destination, 1);
+
+ // A gain node has channelCountMode "max" and channelInterpretation
+ // "speakers", and so will up-mix a mono input when there is stereo input.
+ let gain = new GainNode(context);
+ gain.connect(splitter);
+
+ // The delay node initially outputs a single channel of silence, when it
+ // does not have enough signal in its history to output what it has
+ // previously received. After the delay period, it will then output the
+ // stereo signal it received.
+ let delay =
+ new DelayNode(context,
+ {maxDelayTime: MAX_DELAY_FRAMES / context.sampleRate,
+ delayTime: DELAY_FRAMES / context.sampleRate});
+ // Schedule an increase in the delay to return to mono silent output from
+ // the unfilled portion of the DelayNode's buffer.
+ delay.delayTime.setValueAtTime(MAX_DELAY_FRAMES / context.sampleRate,
+ MONO_OUTPUT_START_FRAME / context.sampleRate);
+ delay.connect(gain);
+
+ let stereoMerger = new ChannelMergerNode(context, {numberOfInputs: 2});
+ stereoMerger.connect(delay);
+
+ let leftOffset = 0.125;
+ let rightOffset = 0.5;
+ let leftSource = new ConstantSourceNode(context, {offset: leftOffset});
+ let rightSource = new ConstantSourceNode(context, {offset: rightOffset});
+ leftSource.start();
+ rightSource.start();
+ leftSource.connect(stereoMerger, 0, 0);
+ rightSource.connect(stereoMerger, 0, 1);
+ // Connect a mono source directly to the gain, so that even stereo silence
+ // will be detected in channel 1 of the gain output because it will cause
+ // the mono source to be up-mixed.
+ let monoOffset = 0.25
+ let monoSource = new ConstantSourceNode(context, {offset: monoOffset});
+ monoSource.start();
+ monoSource.connect(gain);
+
+ return context.startRendering().
+ then((buffer) => {
+ let output = buffer.getChannelData(0);
+
+ function assert_samples_equal(startIndex, length, expected, description)
+ {
+ for (let i = startIndex; i < startIndex + length; ++i) {
+ assert_equals(output[i], expected, description + ` at ${i}`);
+ }
+ }
+
+ assert_samples_equal(0, DELAY_FRAMES - INTERPOLATION_GRACE,
+ 0, "Initial mono");
+ assert_samples_equal(DELAY_FRAMES + INTERPOLATION_GRACE, STEREO_FRAMES,
+ monoOffset + rightOffset, "Stereo");
+ assert_samples_equal(MONO_OUTPUT_START_FRAME + INTERPOLATION_GRACE,
+ MONO_FRAMES,
+ 0, "Final mono");
+ });
+});
+
+</script>