diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/Cue.java b/library/core/src/main/java/com/google/android/exoplayer2/text/Cue.java
index bd617ad626..946af76e53 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/Cue.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/Cue.java
@@ -333,7 +333,7 @@ public class Cue {
    */
   public Cue(
       CharSequence text,
-      Alignment textAlignment,
+      @Nullable Alignment textAlignment,
       float line,
       @LineType int lineType,
       @AnchorType int lineAnchor,
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/SimpleSubtitleDecoder.java b/library/core/src/main/java/com/google/android/exoplayer2/text/SimpleSubtitleDecoder.java
index bd561afaf8..8a1aea179a 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/SimpleSubtitleDecoder.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/SimpleSubtitleDecoder.java
@@ -18,6 +18,7 @@ package com.google.android.exoplayer2.text;
 import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.decoder.SimpleDecoder;
+import com.google.android.exoplayer2.util.Assertions;
 import java.nio.ByteBuffer;
 
 /**
@@ -29,9 +30,8 @@ public abstract class SimpleSubtitleDecoder extends
 
   private final String name;
 
-  /**
-   * @param name The name of the decoder.
-   */
+  /** @param name The name of the decoder. */
+  @SuppressWarnings("initialization:method.invocation.invalid")
   protected SimpleSubtitleDecoder(String name) {
     super(new SubtitleInputBuffer[2], new SubtitleOutputBuffer[2]);
     this.name = name;
@@ -74,7 +74,7 @@ public abstract class SimpleSubtitleDecoder extends
   protected final SubtitleDecoderException decode(
       SubtitleInputBuffer inputBuffer, SubtitleOutputBuffer outputBuffer, boolean reset) {
     try {
-      ByteBuffer inputData = inputBuffer.data;
+      ByteBuffer inputData = Assertions.checkNotNull(inputBuffer.data);
       Subtitle subtitle = decode(inputData.array(), inputData.limit(), reset);
       outputBuffer.setContent(inputBuffer.timeUs, subtitle, inputBuffer.subsampleOffsetUs);
       // Clear BUFFER_FLAG_DECODE_ONLY (see [Internal: b/27893809]).
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/TextRenderer.java b/library/core/src/main/java/com/google/android/exoplayer2/text/TextRenderer.java
index 35e60dcf82..d359eebfdb 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/TextRenderer.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/TextRenderer.java
@@ -80,11 +80,11 @@ public final class TextRenderer extends BaseRenderer implements Callback {
   private boolean inputStreamEnded;
   private boolean outputStreamEnded;
   @ReplacementState private int decoderReplacementState;
-  private Format streamFormat;
-  private SubtitleDecoder decoder;
-  private SubtitleInputBuffer nextInputBuffer;
-  private SubtitleOutputBuffer subtitle;
-  private SubtitleOutputBuffer nextSubtitle;
+  @Nullable private Format streamFormat;
+  @Nullable private SubtitleDecoder decoder;
+  @Nullable private SubtitleInputBuffer nextInputBuffer;
+  @Nullable private SubtitleOutputBuffer subtitle;
+  @Nullable private SubtitleOutputBuffer nextSubtitle;
   private int nextSubtitleEventIndex;
 
   /**
@@ -132,7 +132,7 @@ public final class TextRenderer extends BaseRenderer implements Callback {
   }
 
   @Override
-  protected void onStreamChanged(Format[] formats, long offsetUs) throws ExoPlaybackException {
+  protected void onStreamChanged(Format[] formats, long offsetUs) {
     streamFormat = formats[0];
     if (decoder != null) {
       decoderReplacementState = REPLACEMENT_STATE_SIGNAL_END_OF_STREAM;
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea708Cue.java b/library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea708Cue.java
index fc1f0e2bdc..e04094a8dc 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea708Cue.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea708Cue.java
@@ -24,11 +24,6 @@ import com.google.android.exoplayer2.text.Cue;
  */
 /* package */ final class Cea708Cue extends Cue implements Comparable<Cea708Cue> {
 
-  /**
-   * An unset priority.
-   */
-  public static final int PRIORITY_UNSET = -1;
-
   /**
    * The priority of the cue box.
    */
@@ -64,5 +59,4 @@ import com.google.android.exoplayer2.text.Cue;
     }
     return 0;
   }
-
 }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea708Decoder.java b/library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea708Decoder.java
index b3be88b851..4391bc0bf0 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea708Decoder.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/cea/Cea708Decoder.java
@@ -25,6 +25,7 @@ import android.text.style.BackgroundColorSpan;
 import android.text.style.ForegroundColorSpan;
 import android.text.style.StyleSpan;
 import android.text.style.UnderlineSpan;
+import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.text.Cue;
@@ -152,7 +153,8 @@ public final class Cea708Decoder extends CeaDecoder {
   private DtvCcPacket currentDtvCcPacket;
   private int currentWindow;
 
-  public Cea708Decoder(int accessibilityChannel, List<byte[]> initializationData) {
+  // TODO: Retrieve isWideAspectRatio from initializationData and use it.
+  public Cea708Decoder(int accessibilityChannel, @Nullable List<byte[]> initializationData) {
     ccData = new ParsableByteArray();
     serviceBlockPacket = new ParsableBitArray();
     selectedServiceNumber = accessibilityChannel == Format.NO_VALUE ? 1 : accessibilityChannel;
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/cea/package-info.java b/library/core/src/main/java/com/google/android/exoplayer2/text/cea/package-info.java
new file mode 100644
index 0000000000..cbdf178b6a
--- /dev/null
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/cea/package-info.java
@@ -0,0 +1,19 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+@NonNullApi
+package com.google.android.exoplayer2.text.cea;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/dvb/DvbParser.java b/library/core/src/main/java/com/google/android/exoplayer2/text/dvb/DvbParser.java
index 0e41e4d1b6..8382d9d9d0 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/dvb/DvbParser.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/dvb/DvbParser.java
@@ -22,6 +22,7 @@ import android.graphics.Paint;
 import android.graphics.PorterDuff;
 import android.graphics.PorterDuffXfermode;
 import android.util.SparseArray;
+import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.text.Cue;
 import com.google.android.exoplayer2.util.Log;
 import com.google.android.exoplayer2.util.ParsableBitArray;
@@ -29,6 +30,7 @@ import com.google.android.exoplayer2.util.Util;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 
 /**
  * Parses {@link Cue}s from a DVB subtitle bitstream.
@@ -85,7 +87,7 @@ import java.util.List;
   private final ClutDefinition defaultClutDefinition;
   private final SubtitleService subtitleService;
 
-  private Bitmap bitmap;
+  @MonotonicNonNull private Bitmap bitmap;
 
   /**
    * Construct an instance for the given subtitle and ancillary page ids.
@@ -131,7 +133,8 @@ import java.util.List;
       parseSubtitlingSegment(dataBitArray, subtitleService);
     }
 
-    if (subtitleService.pageComposition == null) {
+    @Nullable PageComposition pageComposition = subtitleService.pageComposition;
+    if (pageComposition == null) {
       return Collections.emptyList();
     }
 
@@ -147,7 +150,7 @@ import java.util.List;
 
     // Build the cues.
     List<Cue> cues = new ArrayList<>();
-    SparseArray<PageRegion> pageRegions = subtitleService.pageComposition.regions;
+    SparseArray<PageRegion> pageRegions = pageComposition.regions;
     for (int i = 0; i < pageRegions.size(); i++) {
       // Save clean clipping state.
       canvas.save();
@@ -182,7 +185,7 @@ import java.util.List;
           objectData = subtitleService.ancillaryObjects.get(objectId);
         }
         if (objectData != null) {
-          Paint paint = objectData.nonModifyingColorFlag ? null : defaultPaint;
+          @Nullable Paint paint = objectData.nonModifyingColorFlag ? null : defaultPaint;
           paintPixelDataSubBlocks(objectData, clutDefinition, regionComposition.depth,
               baseHorizontalAddress + regionObject.horizontalPosition,
               baseVerticalAddress + regionObject.verticalPosition, paint, canvas);
@@ -248,7 +251,7 @@ import java.util.List;
         break;
       case SEGMENT_TYPE_PAGE_COMPOSITION:
         if (pageId == service.subtitlePageId) {
-          PageComposition current = service.pageComposition;
+          @Nullable PageComposition current = service.pageComposition;
           PageComposition pageComposition = parsePageComposition(data, dataFieldLength);
           if (pageComposition.state != PAGE_STATE_NORMAL) {
             service.pageComposition = pageComposition;
@@ -261,11 +264,15 @@ import java.util.List;
         }
         break;
       case SEGMENT_TYPE_REGION_COMPOSITION:
-        PageComposition pageComposition = service.pageComposition;
+        @Nullable PageComposition pageComposition = service.pageComposition;
         if (pageId == service.subtitlePageId && pageComposition != null) {
           RegionComposition regionComposition = parseRegionComposition(data, dataFieldLength);
           if (pageComposition.state == PAGE_STATE_NORMAL) {
-            regionComposition.mergeFrom(service.regions.get(regionComposition.id));
+            @Nullable
+            RegionComposition existingRegionComposition = service.regions.get(regionComposition.id);
+            if (existingRegionComposition != null) {
+              regionComposition.mergeFrom(existingRegionComposition);
+            }
           }
           service.regions.put(regionComposition.id, regionComposition);
         }
@@ -470,8 +477,8 @@ import java.util.List;
     boolean nonModifyingColorFlag = data.readBit();
     data.skipBits(1); // Skip reserved.
 
-    byte[] topFieldData = null;
-    byte[] bottomFieldData = null;
+    @Nullable byte[] topFieldData = null;
+    @Nullable byte[] bottomFieldData = null;
 
     if (objectCodingMethod == OBJECT_CODING_STRING) {
       int numberOfCodes = data.readBits(8);
@@ -577,11 +584,15 @@ import java.util.List;
 
   // Static drawing.
 
-  /**
-   * Draws a pixel data sub-block, as defined by ETSI EN 300 743 7.2.5.1, into a canvas.
-   */
-  private static void paintPixelDataSubBlocks(ObjectData objectData, ClutDefinition clutDefinition,
-      int regionDepth, int horizontalAddress, int verticalAddress, Paint paint, Canvas canvas) {
+  /** Draws a pixel data sub-block, as defined by ETSI EN 300 743 7.2.5.1, into a canvas. */
+  private static void paintPixelDataSubBlocks(
+      ObjectData objectData,
+      ClutDefinition clutDefinition,
+      int regionDepth,
+      int horizontalAddress,
+      int verticalAddress,
+      @Nullable Paint paint,
+      Canvas canvas) {
     int[] clutEntries;
     if (regionDepth == REGION_DEPTH_8_BIT) {
       clutEntries = clutDefinition.clutEntries8Bit;
@@ -596,23 +607,27 @@ import java.util.List;
         verticalAddress + 1, paint, canvas);
   }
 
-  /**
-   * Draws a pixel data sub-block, as defined by ETSI EN 300 743 7.2.5.1, into a canvas.
-   */
-  private static void paintPixelDataSubBlock(byte[] pixelData, int[] clutEntries, int regionDepth,
-      int horizontalAddress, int verticalAddress, Paint paint, Canvas canvas) {
+  /** Draws a pixel data sub-block, as defined by ETSI EN 300 743 7.2.5.1, into a canvas. */
+  private static void paintPixelDataSubBlock(
+      byte[] pixelData,
+      int[] clutEntries,
+      int regionDepth,
+      int horizontalAddress,
+      int verticalAddress,
+      @Nullable Paint paint,
+      Canvas canvas) {
     ParsableBitArray data = new ParsableBitArray(pixelData);
     int column = horizontalAddress;
     int line = verticalAddress;
-    byte[] clutMapTable2To4 = null;
-    byte[] clutMapTable2To8 = null;
-    byte[] clutMapTable4To8 = null;
+    @Nullable byte[] clutMapTable2To4 = null;
+    @Nullable byte[] clutMapTable2To8 = null;
+    @Nullable byte[] clutMapTable4To8 = null;
 
     while (data.bitsLeft() != 0) {
       int dataType = data.readBits(8);
       switch (dataType) {
         case DATA_TYPE_2BP_CODE_STRING:
-          byte[] clutMapTable2ToX;
+          @Nullable byte[] clutMapTable2ToX;
           if (regionDepth == REGION_DEPTH_8_BIT) {
             clutMapTable2ToX = clutMapTable2To8 == null ? defaultMap2To8 : clutMapTable2To8;
           } else if (regionDepth == REGION_DEPTH_4_BIT) {
@@ -625,7 +640,7 @@ import java.util.List;
           data.byteAlign();
           break;
         case DATA_TYPE_4BP_CODE_STRING:
-          byte[] clutMapTable4ToX;
+          @Nullable byte[] clutMapTable4ToX;
           if (regionDepth == REGION_DEPTH_8_BIT) {
             clutMapTable4ToX = clutMapTable4To8 == null ? defaultMap4To8 : clutMapTable4To8;
           } else {
@@ -636,7 +651,9 @@ import java.util.List;
           data.byteAlign();
           break;
         case DATA_TYPE_8BP_CODE_STRING:
-          column = paint8BitPixelCodeString(data, clutEntries, null, column, line, paint, canvas);
+          column =
+              paint8BitPixelCodeString(
+                  data, clutEntries, /* clutMapTable= */ null, column, line, paint, canvas);
           break;
         case DATA_TYPE_24_TABLE_DATA:
           clutMapTable2To4 = buildClutMapTable(4, 4, data);
@@ -658,11 +675,15 @@ import java.util.List;
     }
   }
 
-  /**
-   * Paint a 2-bit/pixel code string, as defined by ETSI EN 300 743 7.2.5.2, to a canvas.
-   */
-  private static int paint2BitPixelCodeString(ParsableBitArray data, int[] clutEntries,
-      byte[] clutMapTable, int column, int line, Paint paint, Canvas canvas) {
+  /** Paint a 2-bit/pixel code string, as defined by ETSI EN 300 743 7.2.5.2, to a canvas. */
+  private static int paint2BitPixelCodeString(
+      ParsableBitArray data,
+      int[] clutEntries,
+      @Nullable byte[] clutMapTable,
+      int column,
+      int line,
+      @Nullable Paint paint,
+      Canvas canvas) {
     boolean endOfPixelCodeString = false;
     do {
       int runLength = 0;
@@ -706,11 +727,15 @@ import java.util.List;
     return column;
   }
 
-  /**
-   * Paint a 4-bit/pixel code string, as defined by ETSI EN 300 743 7.2.5.2, to a canvas.
-   */
-  private static int paint4BitPixelCodeString(ParsableBitArray data, int[] clutEntries,
-      byte[] clutMapTable, int column, int line, Paint paint, Canvas canvas) {
+  /** Paint a 4-bit/pixel code string, as defined by ETSI EN 300 743 7.2.5.2, to a canvas. */
+  private static int paint4BitPixelCodeString(
+      ParsableBitArray data,
+      int[] clutEntries,
+      @Nullable byte[] clutMapTable,
+      int column,
+      int line,
+      @Nullable Paint paint,
+      Canvas canvas) {
     boolean endOfPixelCodeString = false;
     do {
       int runLength = 0;
@@ -760,11 +785,15 @@ import java.util.List;
     return column;
   }
 
-  /**
-   * Paint an 8-bit/pixel code string, as defined by ETSI EN 300 743 7.2.5.2, to a canvas.
-   */
-  private static int paint8BitPixelCodeString(ParsableBitArray data, int[] clutEntries,
-      byte[] clutMapTable, int column, int line, Paint paint, Canvas canvas) {
+  /** Paint an 8-bit/pixel code string, as defined by ETSI EN 300 743 7.2.5.2, to a canvas. */
+  private static int paint8BitPixelCodeString(
+      ParsableBitArray data,
+      int[] clutEntries,
+      @Nullable byte[] clutMapTable,
+      int column,
+      int line,
+      @Nullable Paint paint,
+      Canvas canvas) {
     boolean endOfPixelCodeString = false;
     do {
       int runLength = 0;
@@ -816,18 +845,23 @@ import java.util.List;
     public final int subtitlePageId;
     public final int ancillaryPageId;
 
-    public final SparseArray<RegionComposition> regions = new SparseArray<>();
-    public final SparseArray<ClutDefinition> cluts = new SparseArray<>();
-    public final SparseArray<ObjectData> objects = new SparseArray<>();
-    public final SparseArray<ClutDefinition> ancillaryCluts = new SparseArray<>();
-    public final SparseArray<ObjectData> ancillaryObjects = new SparseArray<>();
+    public final SparseArray<RegionComposition> regions;
+    public final SparseArray<ClutDefinition> cluts;
+    public final SparseArray<ObjectData> objects;
+    public final SparseArray<ClutDefinition> ancillaryCluts;
+    public final SparseArray<ObjectData> ancillaryObjects;
 
-    public DisplayDefinition displayDefinition;
-    public PageComposition pageComposition;
+    @Nullable public DisplayDefinition displayDefinition;
+    @Nullable public PageComposition pageComposition;
 
     public SubtitleService(int subtitlePageId, int ancillaryPageId) {
       this.subtitlePageId = subtitlePageId;
       this.ancillaryPageId = ancillaryPageId;
+      regions = new SparseArray<>();
+      cluts = new SparseArray<>();
+      objects = new SparseArray<>();
+      ancillaryCluts = new SparseArray<>();
+      ancillaryObjects = new SparseArray<>();
     }
 
     public void reset() {
@@ -944,9 +978,6 @@ import java.util.List;
     }
 
     public void mergeFrom(RegionComposition otherRegionComposition) {
-      if (otherRegionComposition == null) {
-        return;
-      }
       SparseArray<RegionObject> otherRegionObjects = otherRegionComposition.regionObjects;
       for (int i = 0; i < otherRegionObjects.size(); i++) {
         regionObjects.put(otherRegionObjects.keyAt(i), otherRegionObjects.valueAt(i));
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/dvb/package-info.java b/library/core/src/main/java/com/google/android/exoplayer2/text/dvb/package-info.java
new file mode 100644
index 0000000000..e5ec87a1a5
--- /dev/null
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/dvb/package-info.java
@@ -0,0 +1,19 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+@NonNullApi
+package com.google.android.exoplayer2.text.dvb;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/package-info.java b/library/core/src/main/java/com/google/android/exoplayer2/text/package-info.java
new file mode 100644
index 0000000000..5c5b3bbc31
--- /dev/null
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/package-info.java
@@ -0,0 +1,19 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+@NonNullApi
+package com.google.android.exoplayer2.text;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/ssa/SsaDecoder.java b/library/core/src/main/java/com/google/android/exoplayer2/text/ssa/SsaDecoder.java
index d751772879..45d4554bb7 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/ssa/SsaDecoder.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/ssa/SsaDecoder.java
@@ -15,6 +15,8 @@
  */
 package com.google.android.exoplayer2.text.ssa;
 
+import static com.google.android.exoplayer2.util.Util.castNonNull;
+
 import android.text.Layout;
 import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.C;
@@ -115,7 +117,7 @@ public final class SsaDecoder extends SimpleSubtitleDecoder {
    * @param data A {@link ParsableByteArray} from which the header should be read.
    */
   private void parseHeader(ParsableByteArray data) {
-    String currentLine;
+    @Nullable String currentLine;
     while ((currentLine = data.readLine()) != null) {
       if ("[Script Info]".equalsIgnoreCase(currentLine)) {
         parseScriptInfo(data);
@@ -140,7 +142,7 @@ public final class SsaDecoder extends SimpleSubtitleDecoder {
    *     set to the beginning of of the first line after {@code [Script Info]}.
    */
   private void parseScriptInfo(ParsableByteArray data) {
-    String currentLine;
+    @Nullable String currentLine;
     while ((currentLine = data.readLine()) != null
         && (data.bytesLeft() == 0 || data.peekUnsignedByte() != '[')) {
       String[] infoNameAndValue = currentLine.split(":");
@@ -176,9 +178,9 @@ public final class SsaDecoder extends SimpleSubtitleDecoder {
    *     at the beginning of of the first line after {@code [V4+ Styles]}.
    */
   private static Map<String, SsaStyle> parseStyles(ParsableByteArray data) {
-    SsaStyle.Format formatInfo = null;
     Map<String, SsaStyle> styles = new LinkedHashMap<>();
-    String currentLine;
+    @Nullable SsaStyle.Format formatInfo = null;
+    @Nullable String currentLine;
     while ((currentLine = data.readLine()) != null
         && (data.bytesLeft() == 0 || data.peekUnsignedByte() != '[')) {
       if (currentLine.startsWith(FORMAT_LINE_PREFIX)) {
@@ -188,7 +190,7 @@ public final class SsaDecoder extends SimpleSubtitleDecoder {
           Log.w(TAG, "Skipping 'Style:' line before 'Format:' line: " + currentLine);
           continue;
         }
-        SsaStyle style = SsaStyle.fromStyleLine(currentLine, formatInfo);
+        @Nullable SsaStyle style = SsaStyle.fromStyleLine(currentLine, formatInfo);
         if (style != null) {
           styles.put(style.name, style);
         }
@@ -205,8 +207,9 @@ public final class SsaDecoder extends SimpleSubtitleDecoder {
    * @param cueTimesUs A sorted list to which parsed cue timestamps will be added.
    */
   private void parseEventBody(ParsableByteArray data, List<List<Cue>> cues, List<Long> cueTimesUs) {
+    @Nullable
     SsaDialogueFormat format = haveInitializationData ? dialogueFormatFromInitializationData : null;
-    String currentLine;
+    @Nullable String currentLine;
     while ((currentLine = data.readLine()) != null) {
       if (currentLine.startsWith(FORMAT_LINE_PREFIX)) {
         format = SsaDialogueFormat.fromFormatLine(currentLine);
@@ -250,6 +253,7 @@ public final class SsaDecoder extends SimpleSubtitleDecoder {
       return;
     }
 
+    @Nullable
     SsaStyle style =
         styles != null && format.styleIndex != C.INDEX_UNSET
             ? styles.get(lineValues[format.styleIndex].trim())
@@ -281,10 +285,11 @@ public final class SsaDecoder extends SimpleSubtitleDecoder {
     if (!matcher.matches()) {
       return C.TIME_UNSET;
     }
-    long timestampUs = Long.parseLong(matcher.group(1)) * 60 * 60 * C.MICROS_PER_SECOND;
-    timestampUs += Long.parseLong(matcher.group(2)) * 60 * C.MICROS_PER_SECOND;
-    timestampUs += Long.parseLong(matcher.group(3)) * C.MICROS_PER_SECOND;
-    timestampUs += Long.parseLong(matcher.group(4)) * 10000; // 100ths of a second.
+    long timestampUs =
+        Long.parseLong(castNonNull(matcher.group(1))) * 60 * 60 * C.MICROS_PER_SECOND;
+    timestampUs += Long.parseLong(castNonNull(matcher.group(2))) * 60 * C.MICROS_PER_SECOND;
+    timestampUs += Long.parseLong(castNonNull(matcher.group(3))) * C.MICROS_PER_SECOND;
+    timestampUs += Long.parseLong(castNonNull(matcher.group(4))) * 10000; // 100ths of a second.
     return timestampUs;
   }
 
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/ssa/package-info.java b/library/core/src/main/java/com/google/android/exoplayer2/text/ssa/package-info.java
new file mode 100644
index 0000000000..cdf891d016
--- /dev/null
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/ssa/package-info.java
@@ -0,0 +1,19 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+@NonNullApi
+package com.google.android.exoplayer2.text.ssa;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/subrip/SubripDecoder.java b/library/core/src/main/java/com/google/android/exoplayer2/text/subrip/SubripDecoder.java
index 20b7efe50a..0c402ac018 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/subrip/SubripDecoder.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/subrip/SubripDecoder.java
@@ -73,8 +73,8 @@ public final class SubripDecoder extends SimpleSubtitleDecoder {
     ArrayList<Cue> cues = new ArrayList<>();
     LongArray cueTimesUs = new LongArray();
     ParsableByteArray subripData = new ParsableByteArray(bytes, length);
-    String currentLine;
 
+    @Nullable String currentLine;
     while ((currentLine = subripData.readLine()) != null) {
       if (currentLine.length() == 0) {
         // Skip blank lines.
@@ -119,7 +119,7 @@ public final class SubripDecoder extends SimpleSubtitleDecoder {
 
       Spanned text = Html.fromHtml(textBuilder.toString());
 
-      String alignmentTag = null;
+      @Nullable String alignmentTag = null;
       for (int i = 0; i < tags.size(); i++) {
         String tag = tags.get(i);
         if (tag.matches(SUBRIP_ALIGNMENT_TAG)) {
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/package-info.java b/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/package-info.java
new file mode 100644
index 0000000000..5b0685e24c
--- /dev/null
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/ttml/package-info.java
@@ -0,0 +1,19 @@
+/*
+ * Copyright (C) 2019 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.
+ */
+@NonNullApi
+package com.google.android.exoplayer2.text.ttml;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCssStyle.java b/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCssStyle.java
index 9186455702..97c0acb1ec 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCssStyle.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCssStyle.java
@@ -220,7 +220,7 @@ public final class WebvttCssStyle {
     return fontFamily;
   }
 
-  public WebvttCssStyle setFontFamily(String fontFamily) {
+  public WebvttCssStyle setFontFamily(@Nullable String fontFamily) {
     this.fontFamily = Util.toLowerInvariant(fontFamily);
     return this;
   }
@@ -264,7 +264,7 @@ public final class WebvttCssStyle {
     return textAlign;
   }
 
-  public WebvttCssStyle setTextAlign(Layout.Alignment textAlign) {
+  public WebvttCssStyle setTextAlign(@Nullable Layout.Alignment textAlign) {
     this.textAlign = textAlign;
     return this;
   }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCue.java b/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCue.java
index eae879c21b..bfa067e322 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCue.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCue.java
@@ -26,9 +26,7 @@ import com.google.android.exoplayer2.util.Log;
 import java.lang.annotation.Documented;
 import java.lang.annotation.Retention;
 
-/**
- * A representation of a WebVTT cue.
- */
+/** A representation of a WebVTT cue. */
 public final class WebvttCue extends Cue {
 
   private static final float DEFAULT_POSITION = 0.5f;
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCueParser.java b/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCueParser.java
index f587d70e90..6e5bd31b4b 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCueParser.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttCueParser.java
@@ -44,9 +44,7 @@ import java.util.List;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
-/**
- * Parser for WebVTT cues. (https://w3c.github.io/webvtt/#cues)
- */
+/** Parser for WebVTT cues. (https://w3c.github.io/webvtt/#cues) */
 public final class WebvttCueParser {
 
   public static final Pattern CUE_HEADER_PATTERN = Pattern
@@ -94,7 +92,7 @@ public final class WebvttCueParser {
    */
   public boolean parseCue(
       ParsableByteArray webvttData, WebvttCue.Builder builder, List<WebvttCssStyle> styles) {
-    String firstLine = webvttData.readLine();
+    @Nullable String firstLine = webvttData.readLine();
     if (firstLine == null) {
       return false;
     }
@@ -104,7 +102,7 @@ public final class WebvttCueParser {
       return parseCue(null, cueHeaderMatcher, webvttData, builder, textBuilder, styles);
     }
     // The first line is not the timestamps, but could be the cue id.
-    String secondLine = webvttData.readLine();
+    @Nullable String secondLine = webvttData.readLine();
     if (secondLine == null) {
       return false;
     }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttParserUtil.java b/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttParserUtil.java
index dce8f8157f..9075083111 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttParserUtil.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/text/webvtt/WebvttParserUtil.java
@@ -52,7 +52,7 @@ public final class WebvttParserUtil {
    * @param input The input from which the line should be read.
    */
   public static boolean isWebvttHeaderLine(ParsableByteArray input) {
-    String line = input.readLine();
+    @Nullable String line = input.readLine();
     return line != null && line.startsWith(WEBVTT_HEADER);
   }
 
@@ -101,7 +101,7 @@ public final class WebvttParserUtil {
    */
   @Nullable
   public static Matcher findNextCueHeader(ParsableByteArray input) {
-    String line;
+    @Nullable String line;
     while ((line = input.readLine()) != null) {
       if (COMMENT.matcher(line).matches()) {
         // Skip until the end of the comment block.