Fix calculation of available duration in DefaultDashChunkSource

The available duration used a "live edge" that was calculated in
the previous iteration and was thus quite old. Also it also used
the end of the last available segment, but the actually available
duration for buffering needs to be clamped to the current live edge
for low-latency streams.

Issue: #4904
PiperOrigin-RevId: 337812621

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

@@ -15,6 +15,7 @@
  */
 package com.google.android.exoplayer2.source.dash;
 
+import static java.lang.Math.max;
 import static java.lang.Math.min;
 
 import android.net.Uri;
@@ -124,9 +125,8 @@ public class DefaultDashChunkSource implements DashChunkSource {
   private TrackSelection trackSelection;
   private DashManifest manifest;
   private int periodIndex;
-  private IOException fatalError;
+  @Nullable private IOException fatalError;
   private boolean missingLastSegment;
-  private long liveEdgeTimeUs;
 
   /**
    * @param manifestLoaderErrorThrower Throws errors affecting loading of manifests.
@@ -172,7 +172,6 @@ public class DefaultDashChunkSource implements DashChunkSource {
     this.playerTrackEmsgHandler = playerTrackEmsgHandler;
 
     long periodDurationUs = manifest.getPeriodDurationUs(periodIndex);
-    liveEdgeTimeUs = C.TIME_UNSET;
 
     List<Representation> representations = getRepresentations();
     representationHolders = new RepresentationHolder[trackSelection.length()];
@@ -266,7 +265,6 @@ public class DefaultDashChunkSource implements DashChunkSource {
     }
 
     long bufferedDurationUs = loadPositionUs - playbackPositionUs;
-    long timeToLiveEdgeUs = resolveTimeToLiveEdgeUs(playbackPositionUs);
     long presentationPositionUs =
         C.msToUs(manifest.availabilityStartTimeMs)
             + C.msToUs(manifest.getPeriod(periodIndex).startMs)
@@ -307,8 +305,9 @@ public class DefaultDashChunkSource implements DashChunkSource {
       }
     }
 
+    long availableLiveDurationUs = getAvailableLiveDurationUs(nowUnixTimeUs, playbackPositionUs);
     trackSelection.updateSelectedTrack(
-        playbackPositionUs, bufferedDurationUs, timeToLiveEdgeUs, queue, chunkIterators);
+        playbackPositionUs, bufferedDurationUs, availableLiveDurationUs, queue, chunkIterators);
 
     RepresentationHolder representationHolder =
         representationHolders[trackSelection.getSelectedIndex()];
@@ -343,9 +342,6 @@ public class DefaultDashChunkSource implements DashChunkSource {
 
     long firstAvailableSegmentNum = representationHolder.getFirstAvailableSegmentNum(nowUnixTimeUs);
     long lastAvailableSegmentNum = representationHolder.getLastAvailableSegmentNum(nowUnixTimeUs);
-
-    updateLiveEdgeTimeUs(representationHolder, lastAvailableSegmentNum);
-
     long segmentNum =
         getSegmentNum(
             representationHolder,
@@ -486,15 +482,17 @@ public class DefaultDashChunkSource implements DashChunkSource {
     return representations;
   }
 
-  private void updateLiveEdgeTimeUs(
-      RepresentationHolder representationHolder, long lastAvailableSegmentNum) {
-    liveEdgeTimeUs = manifest.dynamic
-        ? representationHolder.getSegmentEndTimeUs(lastAvailableSegmentNum) : C.TIME_UNSET;
-  }
-
-  private long resolveTimeToLiveEdgeUs(long playbackPositionUs) {
-    boolean resolveTimeToLiveEdgePossible = manifest.dynamic && liveEdgeTimeUs != C.TIME_UNSET;
-    return resolveTimeToLiveEdgePossible ? liveEdgeTimeUs - playbackPositionUs : C.TIME_UNSET;
+  private long getAvailableLiveDurationUs(long nowUnixTimeUs, long playbackPositionUs) {
+    if (!manifest.dynamic) {
+      return C.TIME_UNSET;
+    }
+    long lastSegmentNum = representationHolders[0].getLastAvailableSegmentNum(nowUnixTimeUs);
+    long lastSegmentEndTimeUs = representationHolders[0].getSegmentEndTimeUs(lastSegmentNum);
+    long nowPeriodTimeUs =
+        nowUnixTimeUs
+            - C.msToUs(manifest.availabilityStartTimeMs + manifest.getPeriod(periodIndex).startMs);
+    long availabilityEndTimeUs = min(nowPeriodTimeUs, lastSegmentEndTimeUs);
+    return max(0, availabilityEndTimeUs - playbackPositionUs);
   }
 
   protected Chunk newInitializationChunk(