test_delaynode-channel-count-1.html

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<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>