Discard all sample data for disabled tracks.

There's a more nuanced version of this where we actually
disable on the loading side, but it's quite tricky to get
the threading just right. I have a change that I'll
probably manage to clean up and send out at some point.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=120106967

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

@@ -146,17 +146,10 @@ public class DefaultTrackOutput implements TrackOutput {
   }
 
   /**
-   * Discards samples from the queue up to the specified time.
-   *
-   * @param timeUs The time up to which samples should be discarded, in microseconds.
+   * Skips all currently buffered samples.
    */
-  public void discardUntil(long timeUs) {
-    while (rollingBuffer.peekSample(sampleBuffer) && sampleBuffer.timeUs < timeUs) {
-      rollingBuffer.skipSample();
-      // We're discarding one or more samples. A subsequent read will need to start at a keyframe.
-      needKeyframe = true;
-    }
-    lastReadTimeUs = Long.MIN_VALUE;
+  public void skipAllSamples() {
+    rollingBuffer.skipAllSamples();
   }
 
   /**

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

@@ -415,7 +415,7 @@ public final class ExtractorSampleSource implements SampleSource, ExtractorOutpu
   @Override
   public void continueBuffering(long playbackPositionUs) {
     downstreamPositionUs = playbackPositionUs;
-    discardSamplesForDisabledTracks(downstreamPositionUs);
+    discardSamplesForDisabledTracks();
   }
 
   @Override
@@ -647,10 +647,10 @@ public final class ExtractorSampleSource implements SampleSource, ExtractorOutpu
     return true;
   }
 
-  private void discardSamplesForDisabledTracks(long timeUs) {
+  private void discardSamplesForDisabledTracks() {
     for (int i = 0; i < trackEnabledStates.length; i++) {
       if (!trackEnabledStates[i]) {
-        sampleQueues.valueAt(i).discardUntil(timeUs);
+        sampleQueues.valueAt(i).skipAllSamples();
       }
     }
   }

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

@@ -153,6 +153,17 @@ import java.util.concurrent.LinkedBlockingDeque;
   }
 
   /**
+   * Skips all currently buffered samples.
+   */
+  public void skipAllSamples() {
+    long nextOffset = infoQueue.skipAllSamples();
+    if (nextOffset == -1) {
+      return;
+    }
+    dropDownstreamTo(nextOffset);
+  }
+
+  /**
    * Attempts to skip to the keyframe before the specified time, if it's present in the buffer.
    *
    * @param timeUs The seek time.
@@ -534,6 +545,25 @@ import java.util.concurrent.LinkedBlockingDeque;
     }
 
     /**
+     * Skips all currently buffered samples.
+     *
+     * @return The absolute position of the first byte in the rolling buffer that may still be
+     *     required after skipping the samples, or -1 if no samples were skipped.
+     */
+    public synchronized long skipAllSamples() {
+      if (queueSize == 0) {
+        return -1;
+      }
+
+      relativeReadIndex = (relativeReadIndex + queueSize) % capacity;
+      absoluteReadIndex += queueSize;
+      queueSize = 0;
+
+      int lastReadIndex = (relativeReadIndex == 0 ? capacity : relativeReadIndex) - 1;
+      return sizes[lastReadIndex] + offsets[lastReadIndex];
+    }
+
+    /**
      * Attempts to locate the keyframe before the specified time, if it's present in the buffer.
      *
      * @param timeUs The seek time.

library/src/main/java/com/google/android/exoplayer/hls/HlsExtractorWrapper.java

@@ -191,16 +191,15 @@ public final class HlsExtractorWrapper implements ExtractorOutput {
   }
 
   /**
-   * Discards samples for the specified track up to the specified time.
+   * Discards all samples for the specified track.
    * <p>
    * This method must only be called after the extractor has been prepared.
    *
    * @param track The track from which samples should be discarded.
-   * @param timeUs The time up to which samples should be discarded, in microseconds.
    */
-  public void discardUntil(int track, long timeUs) {
+  public void discardSamplesForTrack(int track) {
     Assertions.checkState(isPrepared());
-    sampleQueues.valueAt(track).discardUntil(timeUs);
+    sampleQueues.valueAt(track).skipAllSamples();
   }
 
   /**

library/src/main/java/com/google/android/exoplayer/hls/HlsSampleSource.java

@@ -224,7 +224,7 @@ public final class HlsSampleSource implements SampleSource, Loader.Callback {
   public void continueBuffering(long playbackPositionUs) {
     downstreamPositionUs = playbackPositionUs;
     if (!extractors.isEmpty()) {
-      discardSamplesForDisabledTracks(getCurrentExtractor(), downstreamPositionUs);
+      discardSamplesForDisabledTracks(getCurrentExtractor());
     }
     if (!loader.isLoading()) {
       maybeStartLoading();
@@ -570,13 +570,13 @@ public final class HlsSampleSource implements SampleSource, Loader.Callback {
     return extractor;
   }
 
-  private void discardSamplesForDisabledTracks(HlsExtractorWrapper extractor, long timeUs) {
+  private void discardSamplesForDisabledTracks(HlsExtractorWrapper extractor) {
     if (!extractor.isPrepared()) {
       return;
     }
     for (int i = 0; i < groupEnabledStates.length; i++) {
       if (!groupEnabledStates[i]) {
-        extractor.discardUntil(i, timeUs);
+        extractor.discardSamplesForTrack(i);
       }
     }
   }