Ensure only timestamp adjustment masters set first sample timestamps

Without this, it is possible that a non timestamp master instances
the adjuster with its own chunk start time. When chunks are not
aligned, this breaks adjustment.

Issue:#2424

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=149764488

library/src/main/java/com/google/android/exoplayer2/extractor/ts/TsExtractor.java

@@ -383,7 +383,8 @@ public final class TsExtractor implements Extractor {
       if (mode == MODE_SINGLE_PMT || mode == MODE_HLS || remainingPmts == 1) {
         timestampAdjuster = timestampAdjusters.get(0);
       } else {
-        timestampAdjuster = new TimestampAdjuster(timestampAdjusters.get(0).firstSampleTimestampUs);
+        timestampAdjuster = new TimestampAdjuster(
+            timestampAdjusters.get(0).getFirstSampleTimestampUs());
         timestampAdjusters.add(timestampAdjuster);
       }
 

library/src/main/java/com/google/android/exoplayer2/metadata/scte35/SpliceInfoDecoder.java

@@ -88,6 +88,9 @@ public final class SpliceInfoDecoder implements MetadataDecoder {
       case TYPE_PRIVATE_COMMAND:
         command = PrivateCommand.parseFromSection(sectionData, spliceCommandLength, ptsAdjustment);
         break;
+      default:
+        // Do nothing.
+        break;
     }
     return command == null ? new Metadata() : new Metadata(command);
   }

library/src/main/java/com/google/android/exoplayer2/source/hls/HlsChunkSource.java

@@ -282,7 +282,7 @@ import java.util.Locale;
     int discontinuitySequence = mediaPlaylist.discontinuitySequence
         + segment.relativeDiscontinuitySequence;
     TimestampAdjuster timestampAdjuster = timestampAdjusterProvider.getAdjuster(
-        discontinuitySequence, startTimeUs);
+        discontinuitySequence);
 
     // Configure the data source and spec for the chunk.
     Uri chunkUri = UriUtil.resolveToUri(mediaPlaylist.baseUri, segment.url);

library/src/main/java/com/google/android/exoplayer2/source/hls/HlsMediaChunk.java

@@ -242,6 +242,9 @@ import java.util.concurrent.atomic.AtomicInteger;
     }
     if (!isMasterTimestampSource) {
       timestampAdjuster.waitUntilInitialized();
+    } else if (timestampAdjuster.getFirstSampleTimestampUs() == TimestampAdjuster.DO_NOT_OFFSET) {
+      // We're the master and we haven't set the desired first sample timestamp yet.
+      timestampAdjuster.setFirstSampleTimestampUs(startTimeUs);
     }
     try {
       ExtractorInput input = new DefaultExtractorInput(dataSource,

library/src/main/java/com/google/android/exoplayer2/source/hls/TimestampAdjusterProvider.java

@@ -36,13 +36,12 @@ public final class TimestampAdjusterProvider {
    * a chunk with a given discontinuity sequence.
    *
    * @param discontinuitySequence The chunk's discontinuity sequence.
-   * @param startTimeUs The chunk's start time.
    * @return A {@link TimestampAdjuster}.
    */
-  public TimestampAdjuster getAdjuster(int discontinuitySequence, long startTimeUs) {
+  public TimestampAdjuster getAdjuster(int discontinuitySequence) {
     TimestampAdjuster adjuster = timestampAdjusters.get(discontinuitySequence);
     if (adjuster == null) {
-      adjuster = new TimestampAdjuster(startTimeUs);
+      adjuster = new TimestampAdjuster(TimestampAdjuster.DO_NOT_OFFSET);
       timestampAdjusters.put(discontinuitySequence, adjuster);
     }
     return adjuster;

library/src/main/java/com/google/android/exoplayer2/util/TimestampAdjuster.java

@@ -34,21 +34,39 @@ public final class TimestampAdjuster {
    */
   private static final long MAX_PTS_PLUS_ONE = 0x200000000L;
 
-  public final long firstSampleTimestampUs;
-
+  private long firstSampleTimestampUs;
   private long timestampOffsetUs;
 
   // Volatile to allow isInitialized to be called on a different thread to adjustSampleTimestamp.
   private volatile long lastSampleTimestamp;
 
   /**
-   * @param firstSampleTimestampUs The desired result of the first call to
-   *     {@link #adjustSampleTimestamp(long)}, or {@link #DO_NOT_OFFSET} if presentation timestamps
-   *     should not be offset.
+   * @param firstSampleTimestampUs See {@link #setFirstSampleTimestampUs(long)}.
    */
   public TimestampAdjuster(long firstSampleTimestampUs) {
-    this.firstSampleTimestampUs = firstSampleTimestampUs;
     lastSampleTimestamp = C.TIME_UNSET;
+    setFirstSampleTimestampUs(firstSampleTimestampUs);
+  }
+
+  /**
+   * Sets the desired result of the first call to {@link #adjustSampleTimestamp(long)}. Can only be
+   * called before any timestamps have been adjusted.
+   *
+   * @param firstSampleTimestampUs The first adjusted sample timestamp in microseconds, or
+   *     {@link #DO_NOT_OFFSET} if presentation timestamps should not be offset.
+   */
+  public synchronized void setFirstSampleTimestampUs(long firstSampleTimestampUs) {
+    Assertions.checkState(lastSampleTimestamp == C.TIME_UNSET);
+    this.firstSampleTimestampUs = firstSampleTimestampUs;
+  }
+
+  /**
+   * Returns the first adjusted sample timestamp in microseconds.
+   *
+   * @return The first adjusted sample timestamp in microseconds.
+   */
+  public long getFirstSampleTimestampUs() {
+    return firstSampleTimestampUs;
   }
 
   /**