Add nullness annotations to FragmentedMp4Extractor

PiperOrigin-RevId: 327797428

library/common/src/main/java/com/google/android/exoplayer2/util/NalUnitUtil.java

@@ -15,6 +15,7 @@
  */
 package com.google.android.exoplayer2.util;
 
+import androidx.annotation.Nullable;
 import java.nio.ByteBuffer;
 import java.util.Arrays;
 
@@ -219,11 +220,12 @@ public final class NalUnitUtil {
    * Returns whether the NAL unit with the specified header contains supplemental enhancement
    * information.
    *
-   * @param mimeType The sample MIME type.
+   * @param mimeType The sample MIME type, or {@code null} if unknown.
    * @param nalUnitHeaderFirstByte The first byte of nal_unit().
-   * @return Whether the NAL unit with the specified header is an SEI NAL unit.
+   * @return Whether the NAL unit with the specified header is an SEI NAL unit. False is returned if
+   *     the {@code MimeType} is {@code null}.
    */
-  public static boolean isNalUnitSei(String mimeType, byte nalUnitHeaderFirstByte) {
+  public static boolean isNalUnitSei(@Nullable String mimeType, byte nalUnitHeaderFirstByte) {
     return (MimeTypes.VIDEO_H264.equals(mimeType)
         && (nalUnitHeaderFirstByte & 0x1F) == H264_NAL_UNIT_TYPE_SEI)
         || (MimeTypes.VIDEO_H265.equals(mimeType)

library/extractor/src/main/java/com/google/android/exoplayer2/extractor/ExtractorOutput.java

@@ -21,9 +21,33 @@ package com.google.android.exoplayer2.extractor;
 public interface ExtractorOutput {
 
   /**
+   * Placeholder {@link ExtractorOutput} implementation throwing an {@link
+   * UnsupportedOperationException} in each method.
+   */
+  ExtractorOutput PLACEHOLDER =
+      new ExtractorOutput() {
+
+        @Override
+        public TrackOutput track(int id, int type) {
+          throw new UnsupportedOperationException();
+        }
+
+        @Override
+        public void endTracks() {
+          throw new UnsupportedOperationException();
+        }
+
+        @Override
+        public void seekMap(SeekMap seekMap) {
+          throw new UnsupportedOperationException();
+        }
+      };
+
+  /**
    * Called by the {@link Extractor} to get the {@link TrackOutput} for a specific track.
-   * <p>
-   * The same {@link TrackOutput} is returned if multiple calls are made with the same {@code id}.
+   *
+   * <p>The same {@link TrackOutput} is returned if multiple calls are made with the same {@code
+   * id}.
    *
    * @param id A track identifier.
    * @param type The type of the track. Typically one of the {@link com.google.android.exoplayer2.C}