Minimize overlapping chunks if #EXT-X-INDEPENDENT-SEGMENTS is present

It is worth mentioning that the tag can be in the master playlist as well, which
means that it applies to all media playlists. There are a few tags with this
characteristic. This will be addressed in a later CL.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=157210505

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

@@ -222,8 +222,9 @@ import java.util.Locale;
     // Select the chunk.
     int chunkMediaSequence;
     if (previous == null || switchingVariant) {
-      long targetPositionUs = previous == null ? playbackPositionUs : previous.startTimeUs;
-      if (!mediaPlaylist.hasEndTag && targetPositionUs > mediaPlaylist.getEndTimeUs()) {
+      long targetPositionUs = previous == null ? playbackPositionUs
+          : mediaPlaylist.hasIndependentSegmentsTag ? previous.endTimeUs : previous.startTimeUs;
+      if (!mediaPlaylist.hasEndTag && targetPositionUs >= mediaPlaylist.getEndTimeUs()) {
         // If the playlist is too old to contain the chunk, we need to refresh it.
         chunkMediaSequence = mediaPlaylist.mediaSequence + mediaPlaylist.segments.size();
       } else {

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

@@ -87,6 +87,7 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
   public final int mediaSequence;
   public final int version;
   public final long targetDurationUs;
+  public final boolean hasIndependentSegmentsTag;
   public final boolean hasEndTag;
   public final boolean hasProgramDateTime;
   public final Segment initializationSegment;
@@ -96,9 +97,9 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
 
   public HlsMediaPlaylist(@PlaylistType int playlistType, String baseUri, long startOffsetUs,
       long startTimeUs, boolean hasDiscontinuitySequence, int discontinuitySequence,
-      int mediaSequence, int version, long targetDurationUs, boolean hasEndTag,
-      boolean hasProgramDateTime, Segment initializationSegment, List<Segment> segments,
-      List<String> dateRanges) {
+      int mediaSequence, int version, long targetDurationUs, boolean hasIndependentSegmentsTag,
+      boolean hasEndTag, boolean hasProgramDateTime, Segment initializationSegment,
+      List<Segment> segments, List<String> dateRanges) {
     super(baseUri);
     this.playlistType = playlistType;
     this.startTimeUs = startTimeUs;
@@ -107,6 +108,7 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
     this.mediaSequence = mediaSequence;
     this.version = version;
     this.targetDurationUs = targetDurationUs;
+    this.hasIndependentSegmentsTag = hasIndependentSegmentsTag;
     this.hasEndTag = hasEndTag;
     this.hasProgramDateTime = hasProgramDateTime;
     this.initializationSegment = initializationSegment;
@@ -157,8 +159,8 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
    */
   public HlsMediaPlaylist copyWith(long startTimeUs, int discontinuitySequence) {
     return new HlsMediaPlaylist(playlistType, baseUri, startOffsetUs, startTimeUs, true,
-        discontinuitySequence, mediaSequence, version, targetDurationUs, hasEndTag,
-        hasProgramDateTime, initializationSegment, segments, dateRanges);
+        discontinuitySequence, mediaSequence, version, targetDurationUs, hasIndependentSegmentsTag,
+        hasEndTag, hasProgramDateTime, initializationSegment, segments, dateRanges);
   }
 
   /**
@@ -173,7 +175,8 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
     }
     return new HlsMediaPlaylist(playlistType, baseUri, startOffsetUs, startTimeUs,
         hasDiscontinuitySequence, discontinuitySequence, mediaSequence, version, targetDurationUs,
-        true, hasProgramDateTime, initializationSegment, segments, dateRanges);
+        hasIndependentSegmentsTag, true, hasProgramDateTime, initializationSegment, segments,
+        dateRanges);
   }
 
 }

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

@@ -52,6 +52,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
   private static final String TAG_DISCONTINUITY_SEQUENCE = "#EXT-X-DISCONTINUITY-SEQUENCE";
   private static final String TAG_PROGRAM_DATE_TIME = "#EXT-X-PROGRAM-DATE-TIME";
   private static final String TAG_INIT_SEGMENT = "#EXT-X-MAP";
+  private static final String TAG_INDEPENDENT_SEGMENTS = "#EXT-X-INDEPENDENT-SEGMENTS";
   private static final String TAG_MEDIA_DURATION = "#EXTINF";
   private static final String TAG_MEDIA_SEQUENCE = "#EXT-X-MEDIA-SEQUENCE";
   private static final String TAG_START = "#EXT-X-START";
@@ -272,6 +273,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
     int mediaSequence = 0;
     int version = 1; // Default version == 1.
     long targetDurationUs = C.TIME_UNSET;
+    boolean hasIndependentSegmentsTag = false;
     boolean hasEndTag = false;
     Segment initializationSegment = null;
     List<Segment> segments = new ArrayList<>();
@@ -380,14 +382,16 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
           segmentByteRangeOffset += segmentByteRangeLength;
         }
         segmentByteRangeLength = C.LENGTH_UNSET;
+      } else if (line.equals(TAG_INDEPENDENT_SEGMENTS)) {
+        hasIndependentSegmentsTag = true;
       } else if (line.equals(TAG_ENDLIST)) {
         hasEndTag = true;
       }
     }
     return new HlsMediaPlaylist(playlistType, baseUri, startOffsetUs, playlistStartTimeUs,
         hasDiscontinuitySequence, playlistDiscontinuitySequence, mediaSequence, version,
-        targetDurationUs, hasEndTag, playlistStartTimeUs != 0, initializationSegment, segments,
-        dateRanges);
+        targetDurationUs, hasIndependentSegmentsTag, hasEndTag, playlistStartTimeUs != 0,
+        initializationSegment, segments, dateRanges);
   }
 
   private static String parseStringAttr(String line, Pattern pattern) throws ParserException {