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diff --git a/externals/oboe/src/flowgraph/resampler/MultiChannelResampler.cpp b/externals/oboe/src/flowgraph/resampler/MultiChannelResampler.cpp
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+++ b/externals/oboe/src/flowgraph/resampler/MultiChannelResampler.cpp
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+/*
+ * Copyright 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <math.h>
+
+#include "IntegerRatio.h"
+#include "LinearResampler.h"
+#include "MultiChannelResampler.h"
+#include "PolyphaseResampler.h"
+#include "PolyphaseResamplerMono.h"
+#include "PolyphaseResamplerStereo.h"
+#include "SincResampler.h"
+#include "SincResamplerStereo.h"
+
+using namespace RESAMPLER_OUTER_NAMESPACE::resampler;
+
+MultiChannelResampler::MultiChannelResampler(const MultiChannelResampler::Builder &builder)
+        : mNumTaps(builder.getNumTaps())
+        , mX(static_cast<size_t>(builder.getChannelCount())
+                * static_cast<size_t>(builder.getNumTaps()) * 2)
+        , mSingleFrame(builder.getChannelCount())
+        , mChannelCount(builder.getChannelCount())
+        {
+    // Reduce sample rates to the smallest ratio.
+    // For example 44100/48000 would become 147/160.
+    IntegerRatio ratio(builder.getInputRate(), builder.getOutputRate());
+    ratio.reduce();
+    mNumerator = ratio.getNumerator();
+    mDenominator = ratio.getDenominator();
+    mIntegerPhase = mDenominator; // so we start with a write needed
+}
+
+// static factory method
+MultiChannelResampler *MultiChannelResampler::make(int32_t channelCount,
+                                                   int32_t inputRate,
+                                                   int32_t outputRate,
+                                                   Quality quality) {
+    Builder builder;
+    builder.setInputRate(inputRate);
+    builder.setOutputRate(outputRate);
+    builder.setChannelCount(channelCount);
+
+    switch (quality) {
+        case Quality::Fastest:
+            builder.setNumTaps(2);
+            break;
+        case Quality::Low:
+            builder.setNumTaps(4);
+            break;
+        case Quality::Medium:
+        default:
+            builder.setNumTaps(8);
+            break;
+        case Quality::High:
+            builder.setNumTaps(16);
+            break;
+        case Quality::Best:
+            builder.setNumTaps(32);
+            break;
+    }
+
+    // Set the cutoff frequency so that we do not get aliasing when down-sampling.
+    if (inputRate > outputRate) {
+        builder.setNormalizedCutoff(kDefaultNormalizedCutoff);
+    }
+    return builder.build();
+}
+
+MultiChannelResampler *MultiChannelResampler::Builder::build() {
+    if (getNumTaps() == 2) {
+        // Note that this does not do low pass filteringh.
+        return new LinearResampler(*this);
+    }
+    IntegerRatio ratio(getInputRate(), getOutputRate());
+    ratio.reduce();
+    bool usePolyphase = (getNumTaps() * ratio.getDenominator()) <= kMaxCoefficients;
+    if (usePolyphase) {
+        if (getChannelCount() == 1) {
+            return new PolyphaseResamplerMono(*this);
+        } else if (getChannelCount() == 2) {
+            return new PolyphaseResamplerStereo(*this);
+        } else {
+            return new PolyphaseResampler(*this);
+        }
+    } else {
+        // Use less optimized resampler that uses a float phaseIncrement.
+        // TODO mono resampler
+        if (getChannelCount() == 2) {
+            return new SincResamplerStereo(*this);
+        } else {
+            return new SincResampler(*this);
+        }
+    }
+}
+
+void MultiChannelResampler::writeFrame(const float *frame) {
+    // Move cursor before write so that cursor points to last written frame in read.
+    if (--mCursor < 0) {
+        mCursor = getNumTaps() - 1;
+    }
+    float *dest = &mX[static_cast<size_t>(mCursor) * static_cast<size_t>(getChannelCount())];
+    int offset = getNumTaps() * getChannelCount();
+    for (int channel = 0; channel < getChannelCount(); channel++) {
+        // Write twice so we avoid having to wrap when reading.
+        dest[channel] = dest[channel + offset] = frame[channel];
+    }
+}
+
+float MultiChannelResampler::sinc(float radians) {
+    if (fabsf(radians) < 1.0e-9f) return 1.0f;   // avoid divide by zero
+    return sinf(radians) / radians;   // Sinc function
+}
+
+// Generate coefficients in the order they will be used by readFrame().
+// This is more complicated but readFrame() is called repeatedly and should be optimized.
+void MultiChannelResampler::generateCoefficients(int32_t inputRate,
+                                              int32_t outputRate,
+                                              int32_t numRows,
+                                              double phaseIncrement,
+                                              float normalizedCutoff) {
+    mCoefficients.resize(static_cast<size_t>(getNumTaps()) * static_cast<size_t>(numRows));
+    int coefficientIndex = 0;
+    double phase = 0.0; // ranges from 0.0 to 1.0, fraction between samples
+    // Stretch the sinc function for low pass filtering.
+    const float cutoffScaler = (outputRate < inputRate)
+             ? (normalizedCutoff * (float)outputRate / inputRate)
+             : 1.0f; // Do not filter when upsampling.
+    const int numTapsHalf = getNumTaps() / 2; // numTaps must be even.
+    const float numTapsHalfInverse = 1.0f / numTapsHalf;
+    for (int i = 0; i < numRows; i++) {
+        float tapPhase = phase - numTapsHalf;
+        float gain = 0.0; // sum of raw coefficients
+        int gainCursor = coefficientIndex;
+        for (int tap = 0; tap < getNumTaps(); tap++) {
+            float radians = tapPhase * M_PI;
+
+#if MCR_USE_KAISER
+            float window = mKaiserWindow(tapPhase * numTapsHalfInverse);
+#else
+            float window = mCoshWindow(static_cast<double>(tapPhase) * numTapsHalfInverse);
+#endif
+            float coefficient = sinc(radians * cutoffScaler) * window;
+            mCoefficients.at(coefficientIndex++) = coefficient;
+            gain += coefficient;
+            tapPhase += 1.0;
+        }
+        phase += phaseIncrement;
+        while (phase >= 1.0) {
+            phase -= 1.0;
+        }
+
+        // Correct for gain variations.
+        float gainCorrection = 1.0 / gain; // normalize the gain
+        for (int tap = 0; tap < getNumTaps(); tap++) {
+            mCoefficients.at(gainCursor + tap) *= gainCorrection;
+        }
+    }
+}