--- a/dom/media/webaudio/AudioEventTimeline.cpp
+++ b/dom/media/webaudio/AudioEventTimeline.cpp
@@ -32,21 +32,22 @@ static float ExtractValueFromCurve(doubl
   if (t >= startTime + duration) {
     // After the duration, return the last curve value
     return aCurve[aCurveLength - 1];
   }
   double ratio = std::max((t - startTime) / duration, 0.0);
   if (ratio >= 1.0) {
     return aCurve[aCurveLength - 1];
   }
-  uint32_t current = uint32_t(aCurveLength * ratio);
+  uint32_t current = uint32_t(floor((aCurveLength - 1) * ratio));
   uint32_t next = current + 1;
+  double step = duration / double(aCurveLength - 1);
   if (next < aCurveLength) {
-    double t0 = double(current) / double(aCurveLength) * duration ;
-    double t1 = double(next) / double(aCurveLength) * duration ;
+    double t0 = current * step;
+    double t1 = next * step;
     return LinearInterpolate(t0, aCurve[current], t1, aCurve[next], t - startTime);
   } else {
     return aCurve[current];
   }
 }
 
 namespace mozilla {
 namespace dom {

--- a/dom/media/webaudio/compiledtest/TestAudioEventTimeline.cpp
+++ b/dom/media/webaudio/compiledtest/TestAudioEventTimeline.cpp
@@ -97,17 +97,21 @@ typedef AudioEventTimeline Timeline;
 void TestSpecExample()
 {
   // First, run the basic tests
   Timeline timeline(10.0f);
   is(timeline.Value(), 10.0f, "Correct default value returned");
 
   ErrorResultMock rv;
 
-  float curve[] = { -1.0f, 0.0f, 1.0f };
+  uint32_t curveLength = 44100;
+  float* curve = new float[curveLength];
+  for (uint32_t i = 0; i < curveLength; ++i) {
+    curve[i] = sin(M_PI * i / float(curveLength));
+  }
 
   // This test is copied from the example in the Web Audio spec
   const double t0 = 0.0,
                t1 = 0.1,
                t2 = 0.2,
                t3 = 0.3,
                t4 = 0.4,
                t5 = 0.6,
@@ -122,37 +126,38 @@ void TestSpecExample()
   timeline.LinearRampToValueAtTime(1.0f, t3, rv);
   is(rv, NS_OK, "LinearRampToValueAtTime succeeded");
   timeline.LinearRampToValueAtTime(0.15f, t4, rv);
   is(rv, NS_OK, "LinearRampToValueAtTime succeeded");
   timeline.ExponentialRampToValueAtTime(0.75f, t5, rv);
   is(rv, NS_OK, "ExponentialRampToValueAtTime succeeded");
   timeline.ExponentialRampToValueAtTime(0.05f, t6, rv);
   is(rv, NS_OK, "ExponentialRampToValueAtTime succeeded");
-  timeline.SetValueCurveAtTime(curve, ArrayLength(curve), t6, t7 - t6, rv);
+  timeline.SetValueCurveAtTime(curve, curveLength, t6, t7 - t6, rv);
   is(rv, NS_OK, "SetValueCurveAtTime succeeded");
 
   is(timeline.GetValueAtTime(0.0), 0.2f, "Correct value");
   is(timeline.GetValueAtTime(0.05), 0.2f, "Correct value");
   is(timeline.GetValueAtTime(0.1), 0.3f, "Correct value");
   is(timeline.GetValueAtTime(0.15), 0.3f, "Correct value");
   is(timeline.GetValueAtTime(0.2), 0.4f, "Correct value");
   is(timeline.GetValueAtTime(0.25), (0.4f + 1.0f) / 2, "Correct value");
   is(timeline.GetValueAtTime(0.3), 1.0f, "Correct value");
   is(timeline.GetValueAtTime(0.35), (1.0f + 0.15f) / 2, "Correct value");
   is(timeline.GetValueAtTime(0.4), 0.15f, "Correct value");
   is(timeline.GetValueAtTime(0.45), (0.15f * powf(0.75f / 0.15f, 0.05f / 0.2f)), "Correct value");
   is(timeline.GetValueAtTime(0.5), (0.15f * powf(0.75f / 0.15f, 0.5f)), "Correct value");
   is(timeline.GetValueAtTime(0.55), (0.15f * powf(0.75f / 0.15f, 0.15f / 0.2f)), "Correct value");
   is(timeline.GetValueAtTime(0.6), 0.75f, "Correct value");
   is(timeline.GetValueAtTime(0.65), (0.75f * powf(0.05f / 0.75f, 0.5f)), "Correct value");
-  is(timeline.GetValueAtTime(0.7), -1.0f, "Correct value");
-  is(timeline.GetValueAtTime(0.8), 0.0f, "Correct value");
-  is(timeline.GetValueAtTime(0.9), 1.0f, "Correct value");
-  is(timeline.GetValueAtTime(1.0), 1.0f, "Correct value");
+  is(timeline.GetValueAtTime(0.7), 0.0f, "Correct value");
+  is(timeline.GetValueAtTime(0.85), 1.0f, "Correct value");
+  is(timeline.GetValueAtTime(1.0), curve[curveLength - 1], "Correct value");
+
+  delete[] curve;
 }
 
 void TestInvalidEvents()
 {
   static_assert(numeric_limits<float>::has_quiet_NaN, "Platform must have a quiet NaN");
   const float NaN = numeric_limits<float>::quiet_NaN();
   const float Infinity = numeric_limits<float>::infinity();
   Timeline timeline(10.0f);

--- a/dom/media/webaudio/test/test_audioParamSetCurveAtTime.html
+++ b/dom/media/webaudio/test/test_audioParamSetCurveAtTime.html
@@ -25,23 +25,24 @@ var gTest = {
     source.start(0);
     return gain;
   },
   createExpectedBuffers: function(context) {
     this.duration = 1024 / context.sampleRate;
     this.curve = new Float32Array([1.0, 0.5, 0.75, 0.25]);
     var expectedBuffer = context.createBuffer(1, 2048, context.sampleRate);
     var data = expectedBuffer.getChannelData(0);
+    var step = 1024 / 3;
     for (var i = 0; i < 2048; ++i) {
-      if (i < 256) {
-        data[i] = 1.0 - 0.5*i/256;
-      } else if (i < 512) {
-        data[i] = 0.5 + 0.25*(i - 256)/256;
-      } else if (i < 768) {
-        data[i] = 0.75 - 0.5*(i - 512)/256;
+      if (i < step) {
+        data[i] = 1.0 - 0.5*i/step;
+      } else if (i < 2*step) {
+        data[i] = 0.5 + 0.25*(i - step)/step;
+      } else if (i < 3*step) {
+        data[i] = 0.75 - 0.5*(i - 2*step)/step;
       } else {
         data[i] = 0.25;
       }
     }
     return expectedBuffer;
   },
 };
 

--- a/dom/media/webaudio/test/test_audioParamSetCurveAtTimeTwice.html
+++ b/dom/media/webaudio/test/test_audioParamSetCurveAtTimeTwice.html
@@ -42,25 +42,23 @@ var gTest = {
   createExpectedBuffers: function(context) {
     this.duration = 1024 / context.sampleRate;
     this.curve = new Float32Array(100);
     for (var i = 0; i < 100; ++i) {
       this.curve[i] = Math.sin(440 * 2 * Math.PI * i / context.sampleRate);
     }
     var expectedBuffer = context.createBuffer(1, 2048, context.sampleRate);
     for (var i = 0; i < 2048; ++i) {
-      var t = i / context.sampleRate;
-      var current = Math.min(99, Math.floor(100 * Math.min(1.0, (t - T0) / this.duration)));
+      step = 1024.0/99.0;
+      var current = Math.floor(i / step);
       var next = current + 1;
       if (next < this.curve.length) {
-        var t0 = current / this.curve.length * this.duration;
-        var t1 = next / this.curve.length * this.duration;
-        expectedBuffer.getChannelData(0)[i] = linearInterpolate(t0, this.curve[current], t1, this.curve[next], t);
+        expectedBuffer.getChannelData(0)[i] = linearInterpolate(current*step, this.curve[current], next*step, this.curve[next], i);
       } else {
-        expectedBuffer.getChannelData(0)[i] = this.curve[current];
+        expectedBuffer.getChannelData(0)[i] = this.curve[99];
       }
     }
     return expectedBuffer;
   },
 };
 
 runTest();