From d944f32f2454c947b2518b40d9c42c85cc077ed1 Mon Sep 17 00:00:00 2001
From: samrobinson <samrobinson@google.com>
Date: Tue, 5 May 2020 13:04:58 +0100
Subject: [PATCH] Change SilenceSkippingAudioProcessor to not rely on the frame
 MSB.

PiperOrigin-RevId: 309925306
---
 .../audio/SilenceSkippingAudioProcessor.java  | 24 +++++++------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/library/core/src/main/java/com/google/android/exoplayer2/audio/SilenceSkippingAudioProcessor.java b/library/core/src/main/java/com/google/android/exoplayer2/audio/SilenceSkippingAudioProcessor.java
index 2a98d2fb25..454007194f 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/audio/SilenceSkippingAudioProcessor.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/audio/SilenceSkippingAudioProcessor.java
@@ -17,11 +17,13 @@ package com.google.android.exoplayer2.audio;
 
 import androidx.annotation.IntDef;
 import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.util.Assertions;
 import com.google.android.exoplayer2.util.Util;
 import java.lang.annotation.Documented;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
 
 /**
  * An {@link AudioProcessor} that skips silence in the input stream. Input and output are 16-bit
@@ -39,19 +41,9 @@ public final class SilenceSkippingAudioProcessor extends BaseAudioProcessor {
    * not exceed {@link #MINIMUM_SILENCE_DURATION_US}.
    */
   private static final long PADDING_SILENCE_US = 20_000;
-  /**
-   * The absolute level below which an individual PCM sample is classified as silent. Note: the
-   * specified value will be rounded so that the threshold check only depends on the more
-   * significant byte, for efficiency.
-   */
+  /** The absolute level below which an individual PCM sample is classified as silent. */
   private static final short SILENCE_THRESHOLD_LEVEL = 1024;
 
-  /**
-   * Threshold for classifying an individual PCM sample as silent based on its more significant
-   * byte. This is {@link #SILENCE_THRESHOLD_LEVEL} divided by 256 with rounding.
-   */
-  private static final byte SILENCE_THRESHOLD_LEVEL_MSB = (SILENCE_THRESHOLD_LEVEL + 128) >> 8;
-
   /** Trimming states. */
   @Documented
   @Retention(RetentionPolicy.SOURCE)
@@ -325,9 +317,10 @@ public final class SilenceSkippingAudioProcessor extends BaseAudioProcessor {
    * classified as a noisy frame, or the limit of the buffer if no such frame exists.
    */
   private int findNoisePosition(ByteBuffer buffer) {
+    Assertions.checkArgument(buffer.order() == ByteOrder.LITTLE_ENDIAN);
     // The input is in ByteOrder.nativeOrder(), which is little endian on Android.
-    for (int i = buffer.position() + 1; i < buffer.limit(); i += 2) {
-      if (Math.abs(buffer.get(i)) > SILENCE_THRESHOLD_LEVEL_MSB) {
+    for (int i = buffer.position(); i < buffer.limit(); i += 2) {
+      if (Math.abs(buffer.getShort(i)) > SILENCE_THRESHOLD_LEVEL) {
         // Round to the start of the frame.
         return bytesPerFrame * (i / bytesPerFrame);
       }
@@ -340,9 +333,10 @@ public final class SilenceSkippingAudioProcessor extends BaseAudioProcessor {
    * from the byte position to the limit are classified as silent.
    */
   private int findNoiseLimit(ByteBuffer buffer) {
+    Assertions.checkArgument(buffer.order() == ByteOrder.LITTLE_ENDIAN);
     // The input is in ByteOrder.nativeOrder(), which is little endian on Android.
-    for (int i = buffer.limit() - 1; i >= buffer.position(); i -= 2) {
-      if (Math.abs(buffer.get(i)) > SILENCE_THRESHOLD_LEVEL_MSB) {
+    for (int i = buffer.limit() - 2; i >= buffer.position(); i -= 2) {
+      if (Math.abs(buffer.getShort(i)) > SILENCE_THRESHOLD_LEVEL) {
         // Return the start of the next frame.
         return bytesPerFrame * (i / bytesPerFrame) + bytesPerFrame;
       }