Calculate ExtractorSampleSource duration if unknown (playlists #4).

When buffering playlist items after the currently-playing one,
continueBuffering should take a position that is negative because the playback
position is before the start of the source being buffered. This change makes
sure that ExtractorSampleSources always have a known duration when they are
fully buffered, which means that the correct (negative) source-relative
position can be calculated.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=124949409

library/src/main/java/com/google/android/exoplayer/SampleSource.java

@@ -37,7 +37,10 @@ public interface SampleSource {
   boolean prepare(long positionUs) throws IOException;
 
   /**
-   * Returns the duration of the source.
+   * Returns the duration of the source in microseconds, or {@link C#UNSET_TIME_US} if not known.
+   * <p>
+   * If {@link #getBufferedPositionUs()} returns {@link C#END_OF_SOURCE_US}, the duration is
+   * guaranteed to be known.
    * <p>
    * This method should only be called after the source has been prepared.
    *

library/src/main/java/com/google/android/exoplayer/TrackRenderer.java

@@ -109,7 +109,6 @@ public abstract class TrackRenderer implements ExoPlayerComponent {
   private int state;
   private TrackStream stream;
   private long streamOffsetUs;
-  private long maximumTimeUs;
   private boolean readEndOfStream;
   private boolean streamIsFinal;
 
@@ -235,7 +234,6 @@ public abstract class TrackRenderer implements ExoPlayerComponent {
    */
   /* package */ final void reset(long positionUs) throws ExoPlaybackException {
     streamIsFinal = false;
-    maximumTimeUs = C.UNSET_TIME_US;
     onReset(positionUs, false);
   }
 
@@ -261,14 +259,6 @@ public abstract class TrackRenderer implements ExoPlayerComponent {
   }
 
   /**
-   * Returns the maximum buffer timestamp read from the stream since the last reset, or
-   * {@link C#UNSET_TIME_US} if no buffers have been read.
-   */
-  /* package */ final long getMaximumTimeUs() {
-    return maximumTimeUs;
-  }
-
-  /**
    * Signals to the renderer that the current {@link TrackStream} will be the final one supplied
    * before it is next disabled or reset.
    */
@@ -372,9 +362,6 @@ public abstract class TrackRenderer implements ExoPlayerComponent {
         return streamIsFinal ? TrackStream.BUFFER_READ : TrackStream.NOTHING_READ;
       }
       buffer.timeUs += streamOffsetUs;
-      if (buffer.timeUs > maximumTimeUs) {
-        maximumTimeUs = buffer.timeUs;
-      }
     }
     return result;
   }

library/src/main/java/com/google/android/exoplayer/extractor/ExtractorSampleSource.java

@@ -111,6 +111,12 @@ public final class ExtractorSampleSource implements SampleSource, ExtractorOutpu
 
   private static final int MIN_RETRY_COUNT_DEFAULT_FOR_MEDIA = -1;
 
+  /**
+   * When the source's duration is unknown, it is calculated by adding this value to the largest
+   * sample timestamp seen when buffering completes.
+   */
+  private static final long DEFAULT_LAST_SAMPLE_DURATION_US = 10000;
+
   // Lazily initialized default extractor classes in priority order.
   private static List<Class<? extends Extractor>> defaultExtractorClasses;
 
@@ -397,11 +403,7 @@ public final class ExtractorSampleSource implements SampleSource, ExtractorOutpu
     } else if (isPendingReset()) {
       return pendingResetPositionUs;
     } else {
-      long largestQueuedTimestampUs = Long.MIN_VALUE;
-      for (DefaultTrackOutput sampleQueue : sampleQueues) {
-        largestQueuedTimestampUs = Math.max(largestQueuedTimestampUs,
-            sampleQueue.getLargestQueuedTimestampUs());
-      }
+      long largestQueuedTimestampUs = getLargestQueuedTimestampUs();
       return largestQueuedTimestampUs == Long.MIN_VALUE ? lastSeekPositionUs
           : largestQueuedTimestampUs;
     }
@@ -459,6 +461,11 @@ public final class ExtractorSampleSource implements SampleSource, ExtractorOutpu
       long loadDurationMs) {
     copyLengthFromLoader(loadable);
     loadingFinished = true;
+    if (durationUs == C.UNSET_TIME_US) {
+      long largestQueuedTimestampUs = getLargestQueuedTimestampUs();
+      durationUs = largestQueuedTimestampUs == Long.MIN_VALUE ? 0
+          : largestQueuedTimestampUs + DEFAULT_LAST_SAMPLE_DURATION_US;
+    }
   }
 
   @Override
@@ -579,6 +586,15 @@ public final class ExtractorSampleSource implements SampleSource, ExtractorOutpu
     return extractedSamplesCount;
   }
 
+  private long getLargestQueuedTimestampUs() {
+    long largestQueuedTimestampUs = Long.MIN_VALUE;
+    for (DefaultTrackOutput sampleQueue : sampleQueues) {
+      largestQueuedTimestampUs = Math.max(largestQueuedTimestampUs,
+          sampleQueue.getLargestQueuedTimestampUs());
+    }
+    return largestQueuedTimestampUs;
+  }
+
   private boolean haveFormatsForAllTracks() {
     for (DefaultTrackOutput sampleQueue : sampleQueues) {
       if (sampleQueue.getUpstreamFormat() == null) {