1 files changed, 209 insertions, 0 deletions
diff --git a/third_party/webrtc/src/webrtc/modules/audio_processing/aec/aec_resampler.c b/third_party/webrtc/src/webrtc/modules/audio_processing/aec/aec_resampler.c
new file mode 100644
index 00000000..99c39efa
--- /dev/null
+++ b/third_party/webrtc/src/webrtc/modules/audio_processing/aec/aec_resampler.c
@@ -0,0 +1,209 @@
+/*
+ *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+/* Resamples a signal to an arbitrary rate. Used by the AEC to compensate for
+ * clock skew by resampling the farend signal.
+ */
+
+#include "webrtc/modules/audio_processing/aec/aec_resampler.h"
+
+#include <assert.h>
+#include <math.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "webrtc/modules/audio_processing/aec/aec_core.h"
+
+enum {
+  kEstimateLengthFrames = 400
+};
+
+typedef struct {
+  float buffer[kResamplerBufferSize];
+  float position;
+
+  int deviceSampleRateHz;
+  int skewData[kEstimateLengthFrames];
+  int skewDataIndex;
+  float skewEstimate;
+} AecResampler;
+
+static int EstimateSkew(const int* rawSkew,
+                        int size,
+                        int absLimit,
+                        float* skewEst);
+
+void* WebRtcAec_CreateResampler() {
+  return malloc(sizeof(AecResampler));
+}
+
+int WebRtcAec_InitResampler(void* resampInst, int deviceSampleRateHz) {
+  AecResampler* obj = (AecResampler*)resampInst;
+  memset(obj->buffer, 0, sizeof(obj->buffer));
+  obj->position = 0.0;
+
+  obj->deviceSampleRateHz = deviceSampleRateHz;
+  memset(obj->skewData, 0, sizeof(obj->skewData));
+  obj->skewDataIndex = 0;
+  obj->skewEstimate = 0.0;
+
+  return 0;
+}
+
+void WebRtcAec_FreeResampler(void* resampInst) {
+  AecResampler* obj = (AecResampler*)resampInst;
+  free(obj);
+}
+
+void WebRtcAec_ResampleLinear(void* resampInst,
+                              const float* inspeech,
+                              size_t size,
+                              float skew,
+                              float* outspeech,
+                              size_t* size_out) {
+  AecResampler* obj = (AecResampler*)resampInst;
+
+  float* y;
+  float be, tnew;
+  size_t tn, mm;
+
+  assert(size <= 2 * FRAME_LEN);
+  assert(resampInst != NULL);
+  assert(inspeech != NULL);
+  assert(outspeech != NULL);
+  assert(size_out != NULL);
+
+  // Add new frame data in lookahead
+  memcpy(&obj->buffer[FRAME_LEN + kResamplingDelay],
+         inspeech,
+         size * sizeof(inspeech[0]));
+
+  // Sample rate ratio
+  be = 1 + skew;
+
+  // Loop over input frame
+  mm = 0;
+  y = &obj->buffer[FRAME_LEN];  // Point at current frame
+
+  tnew = be * mm + obj->position;
+  tn = (size_t)tnew;
+
+  while (tn < size) {
+
+    // Interpolation
+    outspeech[mm] = y[tn] + (tnew - tn) * (y[tn + 1] - y[tn]);
+    mm++;
+
+    tnew = be * mm + obj->position;
+    tn = (int)tnew;
+  }
+
+  *size_out = mm;
+  obj->position += (*size_out) * be - size;
+
+  // Shift buffer
+  memmove(obj->buffer,
+          &obj->buffer[size],
+          (kResamplerBufferSize - size) * sizeof(obj->buffer[0]));
+}
+
+int WebRtcAec_GetSkew(void* resampInst, int rawSkew, float* skewEst) {
+  AecResampler* obj = (AecResampler*)resampInst;
+  int err = 0;
+
+  if (obj->skewDataIndex < kEstimateLengthFrames) {
+    obj->skewData[obj->skewDataIndex] = rawSkew;
+    obj->skewDataIndex++;
+  } else if (obj->skewDataIndex == kEstimateLengthFrames) {
+    err = EstimateSkew(
+        obj->skewData, kEstimateLengthFrames, obj->deviceSampleRateHz, skewEst);
+    obj->skewEstimate = *skewEst;
+    obj->skewDataIndex++;
+  } else {
+    *skewEst = obj->skewEstimate;
+  }
+
+  return err;
+}
+
+int EstimateSkew(const int* rawSkew,
+                 int size,
+                 int deviceSampleRateHz,
+                 float* skewEst) {
+  const int absLimitOuter = (int)(0.04f * deviceSampleRateHz);
+  const int absLimitInner = (int)(0.0025f * deviceSampleRateHz);
+  int i = 0;
+  int n = 0;
+  float rawAvg = 0;
+  float err = 0;
+  float rawAbsDev = 0;
+  int upperLimit = 0;
+  int lowerLimit = 0;
+  float cumSum = 0;
+  float x = 0;
+  float x2 = 0;
+  float y = 0;
+  float xy = 0;
+  float xAvg = 0;
+  float denom = 0;
+  float skew = 0;
+
+  *skewEst = 0;  // Set in case of error below.
+  for (i = 0; i < size; i++) {
+    if ((rawSkew[i] < absLimitOuter && rawSkew[i] > -absLimitOuter)) {
+      n++;
+      rawAvg += rawSkew[i];
+    }
+  }
+
+  if (n == 0) {
+    return -1;
+  }
+  assert(n > 0);
+  rawAvg /= n;
+
+  for (i = 0; i < size; i++) {
+    if ((rawSkew[i] < absLimitOuter && rawSkew[i] > -absLimitOuter)) {
+      err = rawSkew[i] - rawAvg;
+      rawAbsDev += err >= 0 ? err : -err;
+    }
+  }
+  assert(n > 0);
+  rawAbsDev /= n;
+  upperLimit = (int)(rawAvg + 5 * rawAbsDev + 1);  // +1 for ceiling.
+  lowerLimit = (int)(rawAvg - 5 * rawAbsDev - 1);  // -1 for floor.
+
+  n = 0;
+  for (i = 0; i < size; i++) {
+    if ((rawSkew[i] < absLimitInner && rawSkew[i] > -absLimitInner) ||
+        (rawSkew[i] < upperLimit && rawSkew[i] > lowerLimit)) {
+      n++;
+      cumSum += rawSkew[i];
+      x += n;
+      x2 += n * n;
+      y += cumSum;
+      xy += n * cumSum;
+    }
+  }
+
+  if (n == 0) {
+    return -1;
+  }
+  assert(n > 0);
+  xAvg = x / n;
+  denom = x2 - xAvg * x;
+
+  if (denom != 0) {
+    skew = (xy - xAvg * y) / denom;
+  }
+
+  *skewEst = skew;
+  return 0;
+}