Move calculateAccumulatedTruncationErrorForResampling() to Sonic

This is prework for `Sonic` to provide a precise calculation of output
sample counts, and thus allow `SpeedChangingAudioProcessor` to replace
`getSpeedAdjustedTimeAsync()` with an accurate synchronous calculation.

This is a non functional change.

PiperOrigin-RevId: 690608520

libraries/common/src/main/java/androidx/media3/common/audio/Sonic.java

@@ -19,6 +19,8 @@ package androidx.media3.common.audio;
 import static androidx.media3.common.util.Assertions.checkState;
 import static java.lang.Math.min;
 
+import java.math.BigDecimal;
+import java.math.RoundingMode;
 import java.nio.ShortBuffer;
 import java.util.Arrays;
 
@@ -70,6 +72,38 @@ import java.util.Arrays;
   private int maxDiff;
   private double accumulatedSpeedAdjustmentError;
 
+  /**
+   * Returns expected accumulated truncation error for {@link Sonic}'s resampling algorithm, given
+   * an input length, input sample rate, and resampling rate.
+   *
+   * <p><b>Note:</b> This method is only necessary until we address b/361768785 and fix the
+   * underlying truncation issue.
+   *
+   * @param length Length of input in frames.
+   * @param sampleRate Input sample rate of {@link Sonic} instance.
+   * @param resamplingRate Resampling rate given by {@code pitch * (inputSampleRate /
+   *     outputSampleRate)}.
+   */
+  /* package */ static long calculateAccumulatedTruncationErrorForResampling(
+      BigDecimal length, BigDecimal sampleRate, BigDecimal resamplingRate) {
+    // Calculate number of times that Sonic accumulates truncation error. Set scale to 20 decimal
+    // places, so that division doesn't return an integer.
+    BigDecimal errorCount = length.divide(sampleRate, /* scale= */ 20, RoundingMode.HALF_EVEN);
+
+    // Calculate what truncation error Sonic is accumulating, calculated as:
+    // inputSampleRate / resamplingRate - (int) inputSampleRate / resamplingRate. Set scale to 20
+    // decimal places, so that division doesn't return an integer.
+    BigDecimal individualError =
+        sampleRate.divide(resamplingRate, /* scale */ 20, RoundingMode.HALF_EVEN);
+    individualError =
+        individualError.subtract(individualError.setScale(/* newScale= */ 0, RoundingMode.FLOOR));
+    // Calculate total accumulated error = (int) floor(errorCount * individualError).
+    BigDecimal accumulatedError =
+        errorCount.multiply(individualError).setScale(/* newScale= */ 0, RoundingMode.FLOOR);
+
+    return accumulatedError.longValueExact();
+  }
+
   /**
    * Creates a new Sonic audio stream processor.
    *

libraries/common/src/test/java/androidx/media3/common/audio/RandomParameterizedSonicTest.java

@@ -15,7 +15,7 @@
  */
 package androidx.media3.common.audio;
 
-import static androidx.media3.common.audio.SonicTestingUtils.calculateAccumulatedTruncationErrorForResampling;
+import static androidx.media3.common.audio.Sonic.calculateAccumulatedTruncationErrorForResampling;
 import static androidx.media3.test.utils.TestUtil.generateFloatInRange;
 import static com.google.common.truth.Truth.assertThat;
 import static java.lang.Math.max;

libraries/common/src/test/java/androidx/media3/common/audio/RandomParameterizedSpeedChangingAudioProcessorTest.java

@@ -15,7 +15,7 @@
  */
 package androidx.media3.common.audio;
 
-import static androidx.media3.common.audio.SonicTestingUtils.calculateAccumulatedTruncationErrorForResampling;
+import static androidx.media3.common.audio.Sonic.calculateAccumulatedTruncationErrorForResampling;
 import static androidx.media3.test.utils.TestUtil.buildTestData;
 import static androidx.media3.test.utils.TestUtil.generateFloatInRange;
 import static androidx.media3.test.utils.TestUtil.generateLong;

libraries/common/src/test/java/androidx/media3/common/audio/SonicTest.java

@@ -15,9 +15,11 @@
  */
 package androidx.media3.common.audio;
 
+import static androidx.media3.common.audio.Sonic.calculateAccumulatedTruncationErrorForResampling;
 import static com.google.common.truth.Truth.assertThat;
 
 import androidx.test.ext.junit.runners.AndroidJUnit4;
+import java.math.BigDecimal;
 import java.nio.ShortBuffer;
 import org.junit.Rule;
 import org.junit.Test;
@@ -107,4 +109,19 @@ public class SonicTest {
 
     assertThat(outputBuffer.array()).isEqualTo(new short[] {0, 4, 8});
   }
+
+  @Test
+  public void calculateAccumulatedTruncationErrorForResampling_returnsExpectedSampleCount() {
+    long error =
+        calculateAccumulatedTruncationErrorForResampling(
+            /* length= */ BigDecimal.valueOf(26902000),
+            /* sampleRate= */ BigDecimal.valueOf(48000),
+            /* resamplingRate= */ new BigDecimal(String.valueOf(0.33f)));
+
+    // Individual error = fractional part of (sampleRate / resamplingRate) = 0.54 (periodic)
+    // Error count = length / sampleRate = 560.4583.
+    // Accumulated error = error count * individual error = 560.4583 * 0.54 = 305.
+    // (All calculations are done on BigDecimal rounded to 20 decimal places, unless indicated).
+    assertThat(error).isEqualTo(305);
+  }
 }

libraries/common/src/test/java/androidx/media3/common/audio/SonicTestingUtils.java

@@ -1,66 +0,0 @@
-/*
- * Copyright (C) 2024 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.
- */
-package androidx.media3.common.audio;
-
-import java.math.BigDecimal;
-import java.math.RoundingMode;
-
-/** Testing utils class related to {@link Sonic} */
-/* package */ final class SonicTestingUtils {
-  /**
-   * Returns expected accumulated truncation error for {@link Sonic}'s resampling algorithm, given
-   * an input length, input sample rate, and resampling rate.
-   *
-   * <p><b>Note:</b> This method is only necessary until we address b/361768785 and fix the
-   * underlying truncation issue.
-   *
-   * <p>The accumulated truncation error is calculated as follows:
-   *
-   * <ol>
-   *   <li>Individual truncation error: Divide sample rate by resampling rate, and calculate delta
-   *       between floating point result and truncated int representation.
-   *   <li>Truncation accumulation count: Divide length by sample rate to obtain number of times
-   *       that truncation error accumulates.
-   *   <li>Accumulated truncation error: Multiply results of 1 and 2.
-   * </ol>
-   *
-   * @param length Length of input in frames.
-   * @param sampleRate Input sample rate of {@link Sonic} instance.
-   * @param resamplingRate Resampling rate given by {@code pitch * (inputSampleRate /
-   *     outputSampleRate)}.
-   */
-  public static long calculateAccumulatedTruncationErrorForResampling(
-      BigDecimal length, BigDecimal sampleRate, BigDecimal resamplingRate) {
-    // Calculate number of times that Sonic accumulates truncation error. Set scale to 20 decimal
-    // places, so that division doesn't return an integer.
-    BigDecimal errorCount = length.divide(sampleRate, /* scale= */ 20, RoundingMode.HALF_EVEN);
-
-    // Calculate what truncation error Sonic is accumulating, calculated as:
-    // inputSampleRate / resamplingRate - (int) inputSampleRate / resamplingRate. Set scale to 20
-    // decimal places, so that division doesn't return an integer.
-    BigDecimal individualError =
-        sampleRate.divide(resamplingRate, /* scale */ 20, RoundingMode.HALF_EVEN);
-    individualError =
-        individualError.subtract(individualError.setScale(/* newScale= */ 0, RoundingMode.FLOOR));
-    // Calculate total accumulated error = (int) floor(errorCount * individualError).
-    BigDecimal accumulatedError =
-        errorCount.multiply(individualError).setScale(/* newScale= */ 0, RoundingMode.FLOOR);
-
-    return accumulatedError.longValueExact();
-  }
-
-  private SonicTestingUtils() {}
-}