Tweak live-streaming track selection logic.

Follow-up on the update to ABR logic in AdaptiveTrackSelection for live
streaming case:
- Do not reset liveEdgeTimeUs when user seek to a different position.
- For HlsChunkSource, for non-independent segments, currently the
bufferedDuration calculate will subtract previousChunk's duration. So to make
it work with live-streaming ABR logic, we subtract timeToLiveEdgeUs a similar
amount to compensate for that operation.
- Minor update to DefaultSSChunkSource, only perform TrackSelection when needed
(after checking necessary conditions).

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=169531275

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/DefaultDashChunkSource.java

@@ -181,7 +181,7 @@ public final void getNextChunk(MediaChunk previous, long playbackPositionUs, Chu
     }
 
     long bufferedDurationUs = previous != null ? (previous.endTimeUs - playbackPositionUs) : 0;
-    long timeToLiveEdgeUs = resolveTimeToLiveEdgeUs(playbackPositionUs, previous == null);
+    long timeToLiveEdgeUs = resolveTimeToLiveEdgeUs(playbackPositionUs);
     trackSelection.updateSelectedTrack(bufferedDurationUs, timeToLiveEdgeUs);
 
     RepresentationHolder representationHolder =
@@ -385,9 +385,8 @@ private static Chunk newMediaChunk(RepresentationHolder representationHolder,
     }
   }
 
-  private long resolveTimeToLiveEdgeUs(long playbackPositionUs, boolean isAfterPositionReset) {
-    boolean resolveTimeToLiveEdgePossible = manifest.dynamic
-        && !isAfterPositionReset && liveEdgeTimeUs != C.TIME_UNSET;
+  private long resolveTimeToLiveEdgeUs(long playbackPositionUs) {
+    boolean resolveTimeToLiveEdgePossible = manifest.dynamic && liveEdgeTimeUs != C.TIME_UNSET;
     return resolveTimeToLiveEdgePossible ? liveEdgeTimeUs - playbackPositionUs : C.TIME_UNSET;
   }
 

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

@@ -209,14 +209,24 @@ public void getNextChunk(HlsMediaChunk previous, long playbackPositionUs, HlsChu
     int oldVariantIndex = previous == null ? C.INDEX_UNSET
         : trackGroup.indexOf(previous.trackFormat);
     expectedPlaylistUrl = null;
-    // Unless segments are known to be independent, switching variant will require downloading
-    // overlapping segments. Hence we use the start time of the previous chunk rather than its end
-    // time for this case.
-    long bufferedDurationUs = previous == null ? 0 : Math.max(0,
-        (independentSegments ? previous.endTimeUs : previous.startTimeUs) - playbackPositionUs);
+    long bufferedDurationUs = previous == null ? 0 : previous.endTimeUs - playbackPositionUs;
+
+    long timeToLiveEdgeUs = resolveTimeToLiveEdgeUs(playbackPositionUs);
+    if (previous != null && !independentSegments) {
+      // Unless segments are known to be independent, switching variant will require downloading
+      // overlapping segments. Hence we will subtract previous chunk's duration from buffered
+      // duration.
+      // This may affect the live-streaming adaptive track selection logic, when we are comparing
+      // buffered duration to time to live edge to decide whether to switch. Therefore,
+      // we will subtract this same amount from timeToLiveEdgeUs as well.
+      long subtractedDurationUs = previous.getDurationUs();
+      bufferedDurationUs = Math.max(0, bufferedDurationUs - subtractedDurationUs);
+      if (timeToLiveEdgeUs != C.TIME_UNSET) {
+        timeToLiveEdgeUs = Math.max(0, timeToLiveEdgeUs - subtractedDurationUs);
+      }
+    }
 
     // Select the variant.
-    long timeToLiveEdgeUs = resolveTimeToLiveEdgeUs(playbackPositionUs, previous == null);
     trackSelection.updateSelectedTrack(bufferedDurationUs, timeToLiveEdgeUs);
     int selectedVariantIndex = trackSelection.getSelectedIndexInTrackGroup();
 
@@ -365,9 +375,8 @@ public void onPlaylistBlacklisted(HlsUrl url, long blacklistMs) {
 
   // Private methods.
 
-  private long resolveTimeToLiveEdgeUs(long playbackPositionUs, boolean isAfterPositionReset) {
-    final boolean resolveTimeToLiveEdgePossible = !isAfterPositionReset
-        && liveEdgeTimeUs != C.TIME_UNSET;
+  private long resolveTimeToLiveEdgeUs(long playbackPositionUs) {
+    final boolean resolveTimeToLiveEdgePossible = liveEdgeTimeUs != C.TIME_UNSET;
     return resolveTimeToLiveEdgePossible ? liveEdgeTimeUs - playbackPositionUs : C.TIME_UNSET;
   }
 

library/smoothstreaming/src/main/java/com/google/android/exoplayer2/source/smoothstreaming/DefaultSsChunkSource.java

@@ -154,10 +154,6 @@ public final void getNextChunk(MediaChunk previous, long playbackPositionUs, Chu
       return;
     }
 
-    long bufferedDurationUs = previous != null ? (previous.endTimeUs - playbackPositionUs) : 0;
-    long timeToLiveEdgeUs = resolveTimeToLiveEdgeUs(playbackPositionUs);
-    trackSelection.updateSelectedTrack(bufferedDurationUs, timeToLiveEdgeUs);
-
     StreamElement streamElement = manifest.streamElements[elementIndex];
     if (streamElement.chunkCount == 0) {
       // There aren't any chunks for us to load.
@@ -183,6 +179,10 @@ public final void getNextChunk(MediaChunk previous, long playbackPositionUs, Chu
       return;
     }
 
+    long bufferedDurationUs = previous != null ? (previous.endTimeUs - playbackPositionUs) : 0;
+    long timeToLiveEdgeUs = resolveTimeToLiveEdgeUs(playbackPositionUs);
+    trackSelection.updateSelectedTrack(bufferedDurationUs, timeToLiveEdgeUs);
+
     long chunkStartTimeUs = streamElement.getStartTimeUs(chunkIndex);
     long chunkEndTimeUs = chunkStartTimeUs + streamElement.getChunkDurationUs(chunkIndex);
     int currentAbsoluteChunkIndex = chunkIndex + currentManifestChunkOffset;
@@ -229,10 +229,6 @@ private long resolveTimeToLiveEdgeUs(long playbackPositionUs) {
     }
 
     StreamElement currentElement = manifest.streamElements[elementIndex];
-    if (currentElement.chunkCount == 0) {
-      return C.TIME_UNSET;
-    }
-
     int lastChunkIndex = currentElement.chunkCount - 1;
     long lastChunkEndTimeUs = currentElement.getStartTimeUs(lastChunkIndex)
         + currentElement.getChunkDurationUs(lastChunkIndex);