sub-sample-buffer-stitching.html

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This test has a WPT meta file that disables it given conditions:
- os == "linux" : https://bugzilla.mozilla.org/show_bug.cgi?id=1533762
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- os == "android" : https://bugzilla.mozilla.org/show_bug.cgi?id=1846741
This WPT test may be referenced by the following Test IDs:
- /webaudio/the-audio-api/the-audiobuffersourcenode-interface/sub-sample-buffer-stitching.html - WPT Dashboard Interop Dashboard

<!doctype html>

<html>

  <head>

    <title>

      Test Sub-Sample Accurate Stitching of ABSNs

    </title>

    <script src="/resources/testharness.js"></script>

    <script src="/resources/testharnessreport.js"></script>

    <script src="/webaudio/resources/audit-util.js"></script>

    <script src="/webaudio/resources/audit.js"></script>

  </head>

  <body>

    <script>

      let audit = Audit.createTaskRunner();

      audit.define(

            label: 'buffer-stitching-1',

            description: 'Subsample buffer stitching, same rates'

},

          (task, should) => {

            const sampleRate = 44100;

            const bufferRate = 44100;

            const bufferLength = 30;

            // Experimentally determined thresholds.  DO NOT relax these values

            // to far from these values to make the tests pass.

            const errorThreshold = 9.0957e-5;

            const snrThreshold = 85.580;

            // Informative message

            should(sampleRate, 'Test 1: context.sampleRate')

                .beEqualTo(sampleRate);

            testBufferStitching(sampleRate, bufferRate, bufferLength)

                .then(resultBuffer => {

                  const actual = resultBuffer.getChannelData(0);

                  const expected = resultBuffer.getChannelData(1);

                  should(

                      actual,

                      `Stitched sine-wave buffers at sample rate ${bufferRate}`)

                      .beCloseToArray(

                          expected, {absoluteThreshold: errorThreshold});

                  const SNR = 10 * Math.log10(computeSNR(actual, expected));

                  should(SNR, `SNR (${SNR} dB)`)

                      .beGreaterThanOrEqualTo(snrThreshold);

})

                .then(() => task.done());

});

      audit.define(

            label: 'buffer-stitching-2',

            description: 'Subsample buffer stitching, different rates'

},

          (task, should) => {

            const sampleRate = 44100;

            const bufferRate = 43800;

            const bufferLength = 30;

            // Experimentally determined thresholds.  DO NOT relax these values

            // to far from these values to make the tests pass.

            const errorThreshold = 3.8986e-3;

            const snrThreshold = 65.737;

            // Informative message

            should(sampleRate, 'Test 2: context.sampleRate')

                .beEqualTo(sampleRate);

            testBufferStitching(sampleRate, bufferRate, bufferLength)

                .then(resultBuffer => {

                  const actual = resultBuffer.getChannelData(0);

                  const expected = resultBuffer.getChannelData(1);

                  should(

                      actual,

                      `Stitched sine-wave buffers at sample rate ${bufferRate}`)

                      .beCloseToArray(

                          expected, {absoluteThreshold: errorThreshold});

                  const SNR = 10 * Math.log10(computeSNR(actual, expected));

                  should(SNR, `SNR (${SNR} dB)`)

                      .beGreaterThanOrEqualTo(snrThreshold);

})

                .then(() => task.done());

});

      audit.run();

      // Create graph to test stitching of consecutive ABSNs.  The context rate

      // is |sampleRate|, and the buffers have a fixed length of |bufferLength|

      // and rate of |bufferRate|.  The |bufferRate| should not be too different

      // from |sampleRate| because of interpolation of the buffer to the context

      // rate.

      function testBufferStitching(sampleRate, bufferRate, bufferLength) {

        // The context for testing.  Channel 0 contains the output from

        // stitching all the buffers together, and channel 1 contains the

        // expected output.

        const context = new OfflineAudioContext(

            {numberOfChannels: 2, length: sampleRate, sampleRate: sampleRate});

        const merger = new ChannelMergerNode(

            context, {numberOfInputs: context.destination.channelCount});

        merger.connect(context.destination);

        // The reference is a sine wave at 440 Hz.

        const ref = new OscillatorNode(context, {frequency: 440, type: 'sine'});

        ref.connect(merger, 0, 1);

        ref.start();

        // The test signal is a bunch of short AudioBufferSources containing

        // bits of a sine wave.

        let waveSignal = new Float32Array(context.length);

        const omega = 2 * Math.PI / bufferRate * ref.frequency.value;

        for (let k = 0; k < context.length; ++k) {

          waveSignal[k] = Math.sin(omega * k);

        // Slice the sine wave into many little buffers to be assigned to ABSNs

        // that are started at the appropriate times to produce a final sine

        // wave.

        for (let k = 0; k < context.length; k += bufferLength) {

          const buffer =

              new AudioBuffer({length: bufferLength, sampleRate: bufferRate});

          buffer.copyToChannel(waveSignal.slice(k, k + bufferLength), 0);

          const src = new AudioBufferSourceNode(context, {buffer: buffer});

          src.connect(merger, 0, 0);

          src.start(k / bufferRate);

        return context.startRendering();

    </script>

  </body>

</html>