diff --git a/extensions/cast/src/main/java/com/google/android/exoplayer2/ext/cast/package-info.java b/extensions/cast/src/main/java/com/google/android/exoplayer2/ext/cast/package-info.java
new file mode 100644
index 0000000000..07055905a6
--- /dev/null
+++ b/extensions/cast/src/main/java/com/google/android/exoplayer2/ext/cast/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.ext.cast;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/extensions/cronet/src/main/java/com/google/android/exoplayer2/ext/cronet/package-info.java b/extensions/cronet/src/main/java/com/google/android/exoplayer2/ext/cronet/package-info.java
new file mode 100644
index 0000000000..ec0cf8df05
--- /dev/null
+++ b/extensions/cronet/src/main/java/com/google/android/exoplayer2/ext/cronet/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.ext.cronet;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/extensions/ffmpeg/src/main/java/com/google/android/exoplayer2/ext/ffmpeg/package-info.java b/extensions/ffmpeg/src/main/java/com/google/android/exoplayer2/ext/ffmpeg/package-info.java
new file mode 100644
index 0000000000..a9fedb19cb
--- /dev/null
+++ b/extensions/ffmpeg/src/main/java/com/google/android/exoplayer2/ext/ffmpeg/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.ext.ffmpeg;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/extensions/flac/src/main/java/com/google/android/exoplayer2/ext/flac/package-info.java b/extensions/flac/src/main/java/com/google/android/exoplayer2/ext/flac/package-info.java
new file mode 100644
index 0000000000..ef6da7e3c6
--- /dev/null
+++ b/extensions/flac/src/main/java/com/google/android/exoplayer2/ext/flac/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.ext.flac;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoader.java b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoader.java
index 249271dc61..e37f192c97 100644
--- a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoader.java
+++ b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoader.java
@@ -426,7 +426,7 @@ public final class ImaAdsLoader
    * @deprecated Use {@link ImaAdsLoader.Builder}.
    */
   @Deprecated
-  public ImaAdsLoader(Context context, Uri adTagUri, ImaSdkSettings imaSdkSettings) {
+  public ImaAdsLoader(Context context, Uri adTagUri, @Nullable ImaSdkSettings imaSdkSettings) {
     this(
         context,
         adTagUri,
diff --git a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/package-info.java b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/package-info.java
new file mode 100644
index 0000000000..9a382eb18f
--- /dev/null
+++ b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/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.ext.ima;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/extensions/jobdispatcher/src/main/java/com/google/android/exoplayer2/ext/jobdispatcher/package-info.java b/extensions/jobdispatcher/src/main/java/com/google/android/exoplayer2/ext/jobdispatcher/package-info.java
new file mode 100644
index 0000000000..a66904b505
--- /dev/null
+++ b/extensions/jobdispatcher/src/main/java/com/google/android/exoplayer2/ext/jobdispatcher/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.ext.jobdispatcher;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/extensions/leanback/src/main/java/com/google/android/exoplayer2/ext/leanback/package-info.java b/extensions/leanback/src/main/java/com/google/android/exoplayer2/ext/leanback/package-info.java
new file mode 100644
index 0000000000..79c544fc0f
--- /dev/null
+++ b/extensions/leanback/src/main/java/com/google/android/exoplayer2/ext/leanback/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.ext.leanback;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/extensions/okhttp/src/main/java/com/google/android/exoplayer2/ext/okhttp/package-info.java b/extensions/okhttp/src/main/java/com/google/android/exoplayer2/ext/okhttp/package-info.java
new file mode 100644
index 0000000000..54eb4d5967
--- /dev/null
+++ b/extensions/okhttp/src/main/java/com/google/android/exoplayer2/ext/okhttp/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.ext.okhttp;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/extensions/opus/src/main/java/com/google/android/exoplayer2/ext/opus/package-info.java b/extensions/opus/src/main/java/com/google/android/exoplayer2/ext/opus/package-info.java
new file mode 100644
index 0000000000..0848937fdc
--- /dev/null
+++ b/extensions/opus/src/main/java/com/google/android/exoplayer2/ext/opus/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.ext.opus;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/extensions/rtmp/src/main/java/com/google/android/exoplayer2/ext/rtmp/package-info.java b/extensions/rtmp/src/main/java/com/google/android/exoplayer2/ext/rtmp/package-info.java
new file mode 100644
index 0000000000..cb16630bd3
--- /dev/null
+++ b/extensions/rtmp/src/main/java/com/google/android/exoplayer2/ext/rtmp/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.ext.rtmp;
+
+import com.google.android.exoplayer2.util.NonNullApi;
diff --git a/extensions/workmanager/src/main/java/com/google/android/exoplayer2/ext/workmanager/package-info.java b/extensions/workmanager/src/main/java/com/google/android/exoplayer2/ext/workmanager/package-info.java
new file mode 100644
index 0000000000..7e0e244231
--- /dev/null
+++ b/extensions/workmanager/src/main/java/com/google/android/exoplayer2/ext/workmanager/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.ext.workmanager;
+
+import com.google.android.exoplayer2.util.NonNullApi;