From 02b9d8d8b76fc325b21ea190d48adf29a84a777e Mon Sep 17 00:00:00 2001
From: jbibik <jbibik@google.com>
Date: Tue, 11 Jul 2023 19:29:09 +0100
Subject: [PATCH] `Mp4WebvttParser` implementation - moved from
 `Mp4WebvttDecoder`

`Mp4WebvttDecoder` which used to be `SimpleSubtitleDecoder` will now be called `Mp4WebvttParser` and implement `SubtitleParser` interface. For backwards compatibility, we will have the same functionality provided by `DelegatingSubtitleDecoder` backed-up by a new `Mp4WebvttParser` instance.

PiperOrigin-RevId: 547248157
---
 .../text/SubtitleDecoderFactory.java          |   7 +-
 ...btitleDecoderWithMp4WebvttParserTest.java} |  46 ++--
 ...ebvttDecoder.java => Mp4WebvttParser.java} |  61 +++--
 .../text/webvtt/Mp4WebvttSubtitle.java        |  54 ----
 .../text/webvtt/WebvttCueParser.java          |   5 +-
 .../text/webvtt/Mp4WebvttParserTest.java      | 235 ++++++++++++++++++
 6 files changed, 306 insertions(+), 102 deletions(-)
 rename libraries/{extractor/src/test/java/androidx/media3/extractor/text/webvtt/Mp4WebvttDecoderTest.java => exoplayer/src/test/java/androidx/media3/exoplayer/text/DelegatingSubtitleDecoderWithMp4WebvttParserTest.java} (81%)
 rename libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/{Mp4WebvttDecoder.java => Mp4WebvttParser.java} (64%)
 delete mode 100644 libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/Mp4WebvttSubtitle.java
 create mode 100644 libraries/extractor/src/test/java/androidx/media3/extractor/text/webvtt/Mp4WebvttParserTest.java

diff --git a/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/text/SubtitleDecoderFactory.java b/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/text/SubtitleDecoderFactory.java
index 2cf7703e6c..c59cded4c3 100644
--- a/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/text/SubtitleDecoderFactory.java
+++ b/libraries/exoplayer/src/main/java/androidx/media3/exoplayer/text/SubtitleDecoderFactory.java
@@ -28,7 +28,7 @@ import androidx.media3.extractor.text.ssa.SsaParser;
 import androidx.media3.extractor.text.subrip.SubripParser;
 import androidx.media3.extractor.text.ttml.TtmlDecoder;
 import androidx.media3.extractor.text.tx3g.Tx3gDecoder;
-import androidx.media3.extractor.text.webvtt.Mp4WebvttDecoder;
+import androidx.media3.extractor.text.webvtt.Mp4WebvttParser;
 import androidx.media3.extractor.text.webvtt.WebvttDecoder;
 
 /** A factory for {@link SubtitleDecoder} instances. */
@@ -60,7 +60,7 @@ public interface SubtitleDecoderFactory {
    *
    * <ul>
    *   <li>WebVTT ({@link WebvttDecoder})
-   *   <li>WebVTT (MP4) ({@link Mp4WebvttDecoder})
+   *   <li>WebVTT (MP4) ({@link Mp4WebvttParser})
    *   <li>TTML ({@link TtmlDecoder})
    *   <li>SubRip ({@link SubripParser})
    *   <li>SSA/ASS ({@link SsaParser})
@@ -104,7 +104,8 @@ public interface SubtitleDecoderFactory {
                     "DelegatingSubtitleDecoderWithSsaParser",
                     new SsaParser(format.initializationData));
               case MimeTypes.APPLICATION_MP4VTT:
-                return new Mp4WebvttDecoder();
+                return new DelegatingSubtitleDecoder(
+                    "DelegatingSubtitleDecoderWithMp4WebvttParser", new Mp4WebvttParser());
               case MimeTypes.APPLICATION_TTML:
                 return new TtmlDecoder();
               case MimeTypes.APPLICATION_SUBRIP:
diff --git a/libraries/extractor/src/test/java/androidx/media3/extractor/text/webvtt/Mp4WebvttDecoderTest.java b/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/text/DelegatingSubtitleDecoderWithMp4WebvttParserTest.java
similarity index 81%
rename from libraries/extractor/src/test/java/androidx/media3/extractor/text/webvtt/Mp4WebvttDecoderTest.java
rename to libraries/exoplayer/src/test/java/androidx/media3/exoplayer/text/DelegatingSubtitleDecoderWithMp4WebvttParserTest.java
index 936694bada..e7618a3703 100644
--- a/libraries/extractor/src/test/java/androidx/media3/extractor/text/webvtt/Mp4WebvttDecoderTest.java
+++ b/libraries/exoplayer/src/test/java/androidx/media3/exoplayer/text/DelegatingSubtitleDecoderWithMp4WebvttParserTest.java
@@ -13,14 +13,15 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-package androidx.media3.extractor.text.webvtt;
+package androidx.media3.exoplayer.text;
 
 import static com.google.common.truth.Truth.assertThat;
-import static org.junit.Assert.fail;
+import static org.junit.Assert.assertThrows;
 
 import androidx.media3.common.text.Cue;
 import androidx.media3.extractor.text.Subtitle;
-import androidx.media3.extractor.text.SubtitleDecoderException;
+import androidx.media3.extractor.text.webvtt.Mp4WebvttParser;
+import androidx.media3.extractor.text.webvtt.WebvttCueParser;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import com.google.common.truth.Expect;
 import java.util.List;
@@ -28,9 +29,9 @@ import org.junit.Rule;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
-/** Unit test for {@link Mp4WebvttDecoder}. */
+/** Unit test for a {@link DelegatingSubtitleDecoder} backed by {@link Mp4WebvttParser}. */
 @RunWith(AndroidJUnit4.class)
-public final class Mp4WebvttDecoderTest {
+public final class DelegatingSubtitleDecoderWithMp4WebvttParserTest {
 
   private static final byte[] SINGLE_CUE_SAMPLE = {
     0x00,
@@ -161,8 +162,10 @@ public final class Mp4WebvttDecoderTest {
   // Positive tests.
 
   @Test
-  public void singleCueSample() throws SubtitleDecoderException {
-    Mp4WebvttDecoder decoder = new Mp4WebvttDecoder();
+  public void singleCueSample() {
+    DelegatingSubtitleDecoder decoder =
+        new DelegatingSubtitleDecoder(
+            "DelegatingSubtitleDecoderWithMp4WebvttParser", new Mp4WebvttParser());
     Subtitle result = decoder.decode(SINGLE_CUE_SAMPLE, SINGLE_CUE_SAMPLE.length, false);
     // Line feed must be trimmed by the decoder
     Cue expectedCue = WebvttCueParser.newCueForText("Hello World");
@@ -170,8 +173,10 @@ public final class Mp4WebvttDecoderTest {
   }
 
   @Test
-  public void twoCuesSample() throws SubtitleDecoderException {
-    Mp4WebvttDecoder decoder = new Mp4WebvttDecoder();
+  public void twoCuesSample() {
+    DelegatingSubtitleDecoder decoder =
+        new DelegatingSubtitleDecoder(
+            "DelegatingSubtitleDecoderWithMp4WebvttParser", new Mp4WebvttParser());
     Subtitle result = decoder.decode(DOUBLE_CUE_SAMPLE, DOUBLE_CUE_SAMPLE.length, false);
     Cue firstExpectedCue = WebvttCueParser.newCueForText("Hello World");
     Cue secondExpectedCue = WebvttCueParser.newCueForText("Bye Bye");
@@ -179,25 +184,24 @@ public final class Mp4WebvttDecoderTest {
   }
 
   @Test
-  public void noCueSample() throws SubtitleDecoderException {
-    Mp4WebvttDecoder decoder = new Mp4WebvttDecoder();
+  public void noCueSample() {
+    DelegatingSubtitleDecoder decoder =
+        new DelegatingSubtitleDecoder(
+            "DelegatingSubtitleDecoderWithMp4WebvttParser", new Mp4WebvttParser());
     Subtitle result = decoder.decode(NO_CUE_SAMPLE, NO_CUE_SAMPLE.length, false);
-    assertThat(result.getEventTimeCount()).isEqualTo(1);
-    assertThat(result.getEventTime(0)).isEqualTo(0);
-    assertThat(result.getCues(0)).isEmpty();
+    assertThat(result.getEventTimeCount()).isEqualTo(0);
   }
 
   // Negative tests.
 
   @Test
   public void sampleWithIncompleteHeader() {
-    Mp4WebvttDecoder decoder = new Mp4WebvttDecoder();
-    try {
-      decoder.decode(INCOMPLETE_HEADER_SAMPLE, INCOMPLETE_HEADER_SAMPLE.length, false);
-    } catch (SubtitleDecoderException e) {
-      return;
-    }
-    fail();
+    DelegatingSubtitleDecoder decoder =
+        new DelegatingSubtitleDecoder(
+            "DelegatingSubtitleDecoderWithMp4WebvttParser", new Mp4WebvttParser());
+    assertThrows(
+        IllegalArgumentException.class,
+        () -> decoder.decode(INCOMPLETE_HEADER_SAMPLE, INCOMPLETE_HEADER_SAMPLE.length, false));
   }
 
   // Util methods
diff --git a/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/Mp4WebvttDecoder.java b/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/Mp4WebvttParser.java
similarity index 64%
rename from libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/Mp4WebvttDecoder.java
rename to libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/Mp4WebvttParser.java
index 977eede122..5820e0add5 100644
--- a/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/Mp4WebvttDecoder.java
+++ b/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/Mp4WebvttParser.java
@@ -15,22 +15,25 @@
  */
 package androidx.media3.extractor.text.webvtt;
 
+import static androidx.media3.common.util.Assertions.checkArgument;
+
 import androidx.annotation.Nullable;
+import androidx.media3.common.C;
 import androidx.media3.common.text.Cue;
 import androidx.media3.common.util.ParsableByteArray;
 import androidx.media3.common.util.UnstableApi;
 import androidx.media3.common.util.Util;
-import androidx.media3.extractor.text.SimpleSubtitleDecoder;
-import androidx.media3.extractor.text.Subtitle;
-import androidx.media3.extractor.text.SubtitleDecoderException;
+import androidx.media3.extractor.text.CuesWithTiming;
+import androidx.media3.extractor.text.SubtitleParser;
+import com.google.common.collect.ImmutableList;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 
-/** A {@link SimpleSubtitleDecoder} for Webvtt embedded in a Mp4 container file. */
+/** A {@link SubtitleParser} for Webvtt embedded in a Mp4 container file. */
 @SuppressWarnings("ConstantField")
 @UnstableApi
-public final class Mp4WebvttDecoder extends SimpleSubtitleDecoder {
+public final class Mp4WebvttParser implements SubtitleParser {
 
   private static final int BOX_HEADER_SIZE = 8;
 
@@ -44,43 +47,55 @@ public final class Mp4WebvttDecoder extends SimpleSubtitleDecoder {
   private static final int TYPE_vttc = 0x76747463;
 
   private final ParsableByteArray sampleData;
+  private byte[] dataScratch = Util.EMPTY_BYTE_ARRAY;
 
-  public Mp4WebvttDecoder() {
-    super("Mp4WebvttDecoder");
+  public Mp4WebvttParser() {
     sampleData = new ParsableByteArray();
   }
 
   @Override
-  protected Subtitle decode(byte[] data, int length, boolean reset)
-      throws SubtitleDecoderException {
-    // Webvtt in Mp4 samples have boxes inside of them, so we have to do a traditional box parsing:
-    // first 4 bytes size and then 4 bytes type.
-    sampleData.reset(data, length);
-    List<Cue> resultingCueList = new ArrayList<>();
-    while (sampleData.bytesLeft() > 0) {
-      if (sampleData.bytesLeft() < BOX_HEADER_SIZE) {
-        throw new SubtitleDecoderException("Incomplete Mp4Webvtt Top Level box header found.");
+  public ImmutableList<CuesWithTiming> parse(byte[] data, int offset, int length) {
+    if (offset != 0) {
+      if (dataScratch.length < length) {
+        dataScratch = new byte[length];
       }
+      System.arraycopy(
+          /* src= */ data, /* scrPos= */ offset, /* dest= */ dataScratch, /* destPos= */ 0, length);
+      sampleData.reset(dataScratch, length);
+    } else {
+      sampleData.reset(data, length);
+    }
+    List<Cue> cues = new ArrayList<>();
+    while (sampleData.bytesLeft() > 0) {
+      // Webvtt in Mp4 samples have boxes inside of them, so we have to do a traditional box
+      // parsing: first 4 bytes size and then 4 bytes type.
+      checkArgument(
+          sampleData.bytesLeft() >= BOX_HEADER_SIZE,
+          "Incomplete Mp4Webvtt Top Level box header found.");
       int boxSize = sampleData.readInt();
       int boxType = sampleData.readInt();
       if (boxType == TYPE_vttc) {
-        resultingCueList.add(parseVttCueBox(sampleData, boxSize - BOX_HEADER_SIZE));
+        cues.add(parseVttCueBox(sampleData, boxSize - BOX_HEADER_SIZE));
       } else {
         // Peers of the VTTCueBox are still not supported and are skipped.
         sampleData.skipBytes(boxSize - BOX_HEADER_SIZE);
       }
     }
-    return new Mp4WebvttSubtitle(resultingCueList);
+    return cues.isEmpty()
+        ? ImmutableList.of()
+        : ImmutableList.of(
+            new CuesWithTiming(cues, /* startTimeUs= */ 0, /* durationUs= */ C.TIME_UNSET));
   }
 
-  private static Cue parseVttCueBox(ParsableByteArray sampleData, int remainingCueBoxBytes)
-      throws SubtitleDecoderException {
+  @Override
+  public void reset() {}
+
+  private static Cue parseVttCueBox(ParsableByteArray sampleData, int remainingCueBoxBytes) {
     @Nullable Cue.Builder cueBuilder = null;
     @Nullable CharSequence cueText = null;
     while (remainingCueBoxBytes > 0) {
-      if (remainingCueBoxBytes < BOX_HEADER_SIZE) {
-        throw new SubtitleDecoderException("Incomplete vtt cue box header found.");
-      }
+      checkArgument(
+          remainingCueBoxBytes >= BOX_HEADER_SIZE, "Incomplete vtt cue box header found.");
       int boxSize = sampleData.readInt();
       int boxType = sampleData.readInt();
       remainingCueBoxBytes -= BOX_HEADER_SIZE;
diff --git a/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/Mp4WebvttSubtitle.java b/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/Mp4WebvttSubtitle.java
deleted file mode 100644
index bfa9163887..0000000000
--- a/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/Mp4WebvttSubtitle.java
+++ /dev/null
@@ -1,54 +0,0 @@
-/*
- * Copyright (C) 2016 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.extractor.text.webvtt;
-
-import androidx.media3.common.C;
-import androidx.media3.common.text.Cue;
-import androidx.media3.common.util.Assertions;
-import androidx.media3.extractor.text.Subtitle;
-import java.util.Collections;
-import java.util.List;
-
-/** Representation of a Webvtt subtitle embedded in a MP4 container file. */
-/* package */ final class Mp4WebvttSubtitle implements Subtitle {
-
-  private final List<Cue> cues;
-
-  public Mp4WebvttSubtitle(List<Cue> cueList) {
-    cues = Collections.unmodifiableList(cueList);
-  }
-
-  @Override
-  public int getNextEventTimeIndex(long timeUs) {
-    return timeUs < 0 ? 0 : C.INDEX_UNSET;
-  }
-
-  @Override
-  public int getEventTimeCount() {
-    return 1;
-  }
-
-  @Override
-  public long getEventTime(int index) {
-    Assertions.checkArgument(index == 0);
-    return 0;
-  }
-
-  @Override
-  public List<Cue> getCues(long timeUs) {
-    return timeUs >= 0 ? cues : Collections.emptyList();
-  }
-}
diff --git a/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/WebvttCueParser.java b/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/WebvttCueParser.java
index ff6d0fd298..cbf44a94b6 100644
--- a/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/WebvttCueParser.java
+++ b/libraries/extractor/src/main/java/androidx/media3/extractor/text/webvtt/WebvttCueParser.java
@@ -15,6 +15,7 @@
  */
 package androidx.media3.extractor.text.webvtt;
 
+import static androidx.annotation.VisibleForTesting.PACKAGE_PRIVATE;
 import static java.lang.Math.min;
 import static java.lang.annotation.ElementType.TYPE_USE;
 import static java.lang.annotation.RetentionPolicy.SOURCE;
@@ -36,6 +37,7 @@ import android.text.style.TypefaceSpan;
 import android.text.style.UnderlineSpan;
 import androidx.annotation.IntDef;
 import androidx.annotation.Nullable;
+import androidx.annotation.VisibleForTesting;
 import androidx.media3.common.text.Cue;
 import androidx.media3.common.text.HorizontalTextInVerticalContextSpan;
 import androidx.media3.common.text.RubySpan;
@@ -230,7 +232,8 @@ public final class WebvttCueParser {
   }
 
   /** Create a new {@link Cue} containing {@code text} and with WebVTT default values. */
-  /* package */ static Cue newCueForText(CharSequence text) {
+  @VisibleForTesting(otherwise = PACKAGE_PRIVATE)
+  public static Cue newCueForText(CharSequence text) {
     WebvttCueInfoBuilder infoBuilder = new WebvttCueInfoBuilder();
     infoBuilder.text = text;
     return infoBuilder.toCueBuilder().build();
diff --git a/libraries/extractor/src/test/java/androidx/media3/extractor/text/webvtt/Mp4WebvttParserTest.java b/libraries/extractor/src/test/java/androidx/media3/extractor/text/webvtt/Mp4WebvttParserTest.java
new file mode 100644
index 0000000000..a090c2ef59
--- /dev/null
+++ b/libraries/extractor/src/test/java/androidx/media3/extractor/text/webvtt/Mp4WebvttParserTest.java
@@ -0,0 +1,235 @@
+/*
+ * Copyright (C) 2016 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.extractor.text.webvtt;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.assertThrows;
+
+import androidx.media3.common.text.Cue;
+import androidx.media3.extractor.text.CuesWithTiming;
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+import com.google.common.collect.ImmutableList;
+import com.google.common.truth.Expect;
+import java.util.List;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+/** Unit test for {@link Mp4WebvttParser}. */
+@RunWith(AndroidJUnit4.class)
+public final class Mp4WebvttParserTest {
+
+  private static final byte[] SINGLE_CUE_SAMPLE = {
+    0x00,
+    0x00,
+    0x00,
+    0x1C, // Size
+    0x76,
+    0x74,
+    0x74,
+    0x63, // "vttc" Box type. VTT Cue box begins:
+    0x00,
+    0x00,
+    0x00,
+    0x14, // Contained payload box's size
+    0x70,
+    0x61,
+    0x79,
+    0x6c, // Contained payload box's type (payl), Cue Payload Box begins:
+    0x48,
+    0x65,
+    0x6c,
+    0x6c,
+    0x6f,
+    0x20,
+    0x57,
+    0x6f,
+    0x72,
+    0x6c,
+    0x64,
+    0x0a // Hello World\n
+  };
+
+  private static final byte[] DOUBLE_CUE_SAMPLE = {
+    0x00,
+    0x00,
+    0x00,
+    0x1B, // Size
+    0x76,
+    0x74,
+    0x74,
+    0x63, // "vttc" Box type. First VTT Cue box begins:
+    0x00,
+    0x00,
+    0x00,
+    0x13, // First contained payload box's size
+    0x70,
+    0x61,
+    0x79,
+    0x6c, // First contained payload box's type (payl), Cue Payload Box begins:
+    0x48,
+    0x65,
+    0x6c,
+    0x6c,
+    0x6f,
+    0x20,
+    0x57,
+    0x6f,
+    0x72,
+    0x6c,
+    0x64, // Hello World
+    0x00,
+    0x00,
+    0x00,
+    0x17, // Size
+    0x76,
+    0x74,
+    0x74,
+    0x63, // "vttc" Box type. Second VTT Cue box begins:
+    0x00,
+    0x00,
+    0x00,
+    0x0F, // Contained payload box's size
+    0x70,
+    0x61,
+    0x79,
+    0x6c, // Contained payload box's type (payl), Payload begins:
+    0x42,
+    0x79,
+    0x65,
+    0x20,
+    0x42,
+    0x79,
+    0x65 // Bye Bye
+  };
+
+  private static final byte[] NO_CUE_SAMPLE = {
+    0x00,
+    0x00,
+    0x00,
+    0x1B, // Size
+    0x74,
+    0x74,
+    0x74,
+    0x63, // "tttc" Box type, which is not a Cue. Should be skipped:
+    0x00,
+    0x00,
+    0x00,
+    0x13, // Contained payload box's size
+    0x70,
+    0x61,
+    0x79,
+    0x6c, // Contained payload box's type (payl), Cue Payload Box begins:
+    0x48,
+    0x65,
+    0x6c,
+    0x6c,
+    0x6f,
+    0x20,
+    0x57,
+    0x6f,
+    0x72,
+    0x6c,
+    0x64 // Hello World
+  };
+
+  private static final byte[] INCOMPLETE_HEADER_SAMPLE = {
+    0x00, 0x00, 0x00, 0x23, // Size
+    0x76, 0x74, 0x74, 0x63, // "vttc" Box type. VTT Cue box begins:
+    0x00, 0x00, 0x00, 0x14, // Contained payload box's size
+    0x70, 0x61, 0x79, 0x6c, // Contained payload box's type (payl), Cue Payload Box begins:
+    0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x57, 0x6f, 0x72, 0x6c, 0x64, 0x0a, // Hello World\n
+    0x00, 0x00, 0x00, 0x07, // Size of an incomplete header, which belongs to the first vttc box.
+    0x76, 0x74, 0x74
+  };
+
+  @Rule public final Expect expect = Expect.create();
+
+  // Positive tests.
+
+  @Test
+  public void singleCueSample() {
+    Mp4WebvttParser parser = new Mp4WebvttParser();
+    List<CuesWithTiming> result = parser.parse(SINGLE_CUE_SAMPLE);
+    // Line feed must be trimmed by the decoder
+    Cue expectedCue = WebvttCueParser.newCueForText("Hello World");
+    assertMp4WebvttSubtitleEquals(result, expectedCue);
+  }
+
+  @Test
+  public void twoCuesSample() {
+    Mp4WebvttParser parser = new Mp4WebvttParser();
+    List<CuesWithTiming> result = parser.parse(DOUBLE_CUE_SAMPLE);
+    Cue firstExpectedCue = WebvttCueParser.newCueForText("Hello World");
+    Cue secondExpectedCue = WebvttCueParser.newCueForText("Bye Bye");
+    assertMp4WebvttSubtitleEquals(result, firstExpectedCue, secondExpectedCue);
+  }
+
+  @Test
+  public void noCueSample() {
+    Mp4WebvttParser parser = new Mp4WebvttParser();
+    List<CuesWithTiming> result = parser.parse(NO_CUE_SAMPLE);
+    assertThat(result).isEmpty();
+  }
+
+  // Negative tests.
+
+  @Test
+  public void sampleWithIncompleteHeader() {
+    Mp4WebvttParser parser = new Mp4WebvttParser();
+    assertThrows(IllegalArgumentException.class, () -> parser.parse(INCOMPLETE_HEADER_SAMPLE));
+  }
+
+  // Util methods
+
+  /**
+   * Asserts that the Subtitle's cues (which are all part of the event at t=0) are equal to the
+   * expected Cues.
+   *
+   * @param cuesWithTimings The list of {@link CuesWithTiming} to check.
+   * @param expectedCues The expected {@link Cue}s.
+   */
+  private void assertMp4WebvttSubtitleEquals(
+      List<CuesWithTiming> cuesWithTimings, Cue... expectedCues) {
+    assertThat(cuesWithTimings).hasSize(1);
+    assertThat(cuesWithTimings.get(0).startTimeUs).isEqualTo(0);
+    ImmutableList<Cue> allCues = cuesWithTimings.get(0).cues;
+    assertThat(allCues).hasSize(expectedCues.length);
+    for (int i = 0; i < allCues.size(); i++) {
+      assertCuesEqual(expectedCues[i], allCues.get(i));
+    }
+  }
+
+  /** Asserts that two cues are equal. */
+  private void assertCuesEqual(Cue expected, Cue actual) {
+    expect.withMessage("Cue.line").that(actual.line).isEqualTo(expected.line);
+    expect.withMessage("Cue.lineAnchor").that(actual.lineAnchor).isEqualTo(expected.lineAnchor);
+    expect.withMessage("Cue.lineType").that(actual.lineType).isEqualTo(expected.lineType);
+    expect.withMessage("Cue.position").that(actual.position).isEqualTo(expected.position);
+    expect
+        .withMessage("Cue.positionAnchor")
+        .that(actual.positionAnchor)
+        .isEqualTo(expected.positionAnchor);
+    expect.withMessage("Cue.size").that(actual.size).isEqualTo(expected.size);
+    expect.withMessage("Cue.text").that(actual.text.toString()).isEqualTo(expected.text.toString());
+    expect
+        .withMessage("Cue.textAlignment")
+        .that(actual.textAlignment)
+        .isEqualTo(expected.textAlignment);
+
+    assertThat(expect.hasFailures()).isFalse();
+  }
+}