Track HLS discontinuities when playlist does not declare sequence

This is an initial version that does not handle cross-playlists
adjustment in an ideal way.

Issue:#1789

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=144692969

library/src/androidTest/java/com/google/android/exoplayer2/source/hls/playlist/HlsMediaPlaylistParserTest.java

@@ -17,6 +17,7 @@
 
 import android.net.Uri;
 import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.source.hls.playlist.HlsMediaPlaylist.Segment;
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
@@ -73,59 +74,64 @@ public void testParseMediaPlaylist() {
 
       assertEquals(2679, mediaPlaylist.mediaSequence);
       assertEquals(3, mediaPlaylist.version);
-      assertEquals(true, mediaPlaylist.hasEndTag);
-      List<HlsMediaPlaylist.Segment> segments = mediaPlaylist.segments;
+      assertTrue(mediaPlaylist.hasEndTag);
+      List<Segment> segments = mediaPlaylist.segments;
       assertNotNull(segments);
       assertEquals(5, segments.size());
 
-      assertEquals(4, segments.get(0).discontinuitySequenceNumber);
-      assertEquals(7975000, segments.get(0).durationUs);
-      assertEquals(false, segments.get(0).isEncrypted);
-      assertEquals(null, segments.get(0).encryptionKeyUri);
-      assertEquals(null, segments.get(0).encryptionIV);
-      assertEquals(51370, segments.get(0).byterangeLength);
-      assertEquals(0, segments.get(0).byterangeOffset);
-      assertEquals("https://priv.example.com/fileSequence2679.ts", segments.get(0).url);
+      Segment segment = segments.get(0);
+      assertEquals(4, mediaPlaylist.discontinuitySequence + segment.relativeDiscontinuitySequence);
+      assertEquals(7975000, segment.durationUs);
+      assertFalse(segment.isEncrypted);
+      assertEquals(null, segment.encryptionKeyUri);
+      assertEquals(null, segment.encryptionIV);
+      assertEquals(51370, segment.byterangeLength);
+      assertEquals(0, segment.byterangeOffset);
+      assertEquals("https://priv.example.com/fileSequence2679.ts", segment.url);
 
-      assertEquals(4, segments.get(1).discontinuitySequenceNumber);
-      assertEquals(7975000, segments.get(1).durationUs);
-      assertEquals(true, segments.get(1).isEncrypted);
-      assertEquals("https://priv.example.com/key.php?r=2680", segments.get(1).encryptionKeyUri);
-      assertEquals("0x1566B", segments.get(1).encryptionIV);
-      assertEquals(51501, segments.get(1).byterangeLength);
-      assertEquals(2147483648L, segments.get(1).byterangeOffset);
-      assertEquals("https://priv.example.com/fileSequence2680.ts", segments.get(1).url);
+      segment = segments.get(1);
+      assertEquals(0, segment.relativeDiscontinuitySequence);
+      assertEquals(7975000, segment.durationUs);
+      assertTrue(segment.isEncrypted);
+      assertEquals("https://priv.example.com/key.php?r=2680", segment.encryptionKeyUri);
+      assertEquals("0x1566B", segment.encryptionIV);
+      assertEquals(51501, segment.byterangeLength);
+      assertEquals(2147483648L, segment.byterangeOffset);
+      assertEquals("https://priv.example.com/fileSequence2680.ts", segment.url);
 
-      assertEquals(4, segments.get(2).discontinuitySequenceNumber);
-      assertEquals(7941000, segments.get(2).durationUs);
-      assertEquals(false, segments.get(2).isEncrypted);
-      assertEquals(null, segments.get(2).encryptionKeyUri);
-      assertEquals(null, segments.get(2).encryptionIV);
-      assertEquals(51501, segments.get(2).byterangeLength);
-      assertEquals(2147535149L, segments.get(2).byterangeOffset);
-      assertEquals("https://priv.example.com/fileSequence2681.ts", segments.get(2).url);
+      segment = segments.get(2);
+      assertEquals(0, segment.relativeDiscontinuitySequence);
+      assertEquals(7941000, segment.durationUs);
+      assertFalse(segment.isEncrypted);
+      assertEquals(null, segment.encryptionKeyUri);
+      assertEquals(null, segment.encryptionIV);
+      assertEquals(51501, segment.byterangeLength);
+      assertEquals(2147535149L, segment.byterangeOffset);
+      assertEquals("https://priv.example.com/fileSequence2681.ts", segment.url);
 
-      assertEquals(5, segments.get(3).discontinuitySequenceNumber);
-      assertEquals(7975000, segments.get(3).durationUs);
-      assertEquals(true, segments.get(3).isEncrypted);
-      assertEquals("https://priv.example.com/key.php?r=2682", segments.get(3).encryptionKeyUri);
+      segment = segments.get(3);
+      assertEquals(1, segment.relativeDiscontinuitySequence);
+      assertEquals(7975000, segment.durationUs);
+      assertTrue(segment.isEncrypted);
+      assertEquals("https://priv.example.com/key.php?r=2682", segment.encryptionKeyUri);
       // 0xA7A == 2682.
-      assertNotNull(segments.get(3).encryptionIV);
-      assertEquals("A7A", segments.get(3).encryptionIV.toUpperCase(Locale.getDefault()));
-      assertEquals(51740, segments.get(3).byterangeLength);
-      assertEquals(2147586650L, segments.get(3).byterangeOffset);
-      assertEquals("https://priv.example.com/fileSequence2682.ts", segments.get(3).url);
+      assertNotNull(segment.encryptionIV);
+      assertEquals("A7A", segment.encryptionIV.toUpperCase(Locale.getDefault()));
+      assertEquals(51740, segment.byterangeLength);
+      assertEquals(2147586650L, segment.byterangeOffset);
+      assertEquals("https://priv.example.com/fileSequence2682.ts", segment.url);
 
-      assertEquals(5, segments.get(4).discontinuitySequenceNumber);
-      assertEquals(7975000, segments.get(4).durationUs);
-      assertEquals(true, segments.get(4).isEncrypted);
-      assertEquals("https://priv.example.com/key.php?r=2682", segments.get(4).encryptionKeyUri);
+      segment = segments.get(4);
+      assertEquals(1, segment.relativeDiscontinuitySequence);
+      assertEquals(7975000, segment.durationUs);
+      assertTrue(segment.isEncrypted);
+      assertEquals("https://priv.example.com/key.php?r=2682", segment.encryptionKeyUri);
       // 0xA7B == 2683.
-      assertNotNull(segments.get(4).encryptionIV);
-      assertEquals("A7B", segments.get(4).encryptionIV.toUpperCase(Locale.getDefault()));
-      assertEquals(C.LENGTH_UNSET, segments.get(4).byterangeLength);
-      assertEquals(0, segments.get(4).byterangeOffset);
-      assertEquals("https://priv.example.com/fileSequence2683.ts", segments.get(4).url);
+      assertNotNull(segment.encryptionIV);
+      assertEquals("A7B", segment.encryptionIV.toUpperCase(Locale.getDefault()));
+      assertEquals(C.LENGTH_UNSET, segment.byterangeLength);
+      assertEquals(0, segment.byterangeOffset);
+      assertEquals("https://priv.example.com/fileSequence2683.ts", segment.url);
     } catch (IOException exception) {
       fail(exception.getMessage());
     }

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

@@ -270,18 +270,19 @@ public void getNextChunk(HlsMediaChunk previous, long playbackPositionUs, HlsChu
 
     // Compute start time of the next chunk.
     long startTimeUs = mediaPlaylist.startTimeUs + segment.relativeStartTimeUs;
+    int discontinuitySequence = mediaPlaylist.discontinuitySequence
+        + segment.relativeDiscontinuitySequence;
     TimestampAdjuster timestampAdjuster = timestampAdjusterProvider.getAdjuster(
-        segment.discontinuitySequenceNumber, startTimeUs);
+        discontinuitySequence, startTimeUs);
 
     // Configure the data source and spec for the chunk.
     Uri chunkUri = UriUtil.resolveToUri(mediaPlaylist.baseUri, segment.url);
     DataSpec dataSpec = new DataSpec(chunkUri, segment.byterangeOffset, segment.byterangeLength,
         null);
     out.chunk = new HlsMediaChunk(dataSource, dataSpec, initDataSpec, variants[newVariantIndex],
         trackSelection.getSelectionReason(), trackSelection.getSelectionData(),
-        startTimeUs, startTimeUs + segment.durationUs, chunkMediaSequence,
-        segment.discontinuitySequenceNumber, isTimestampMaster, timestampAdjuster, previous,
-        encryptionKey, encryptionIv);
+        startTimeUs, startTimeUs + segment.durationUs, chunkMediaSequence, discontinuitySequence,
+        isTimestampMaster, timestampAdjuster, previous, encryptionKey, encryptionIv);
   }
 
   /**

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

@@ -31,7 +31,7 @@ public static final class Segment implements Comparable<Long> {
 
     public final String url;
     public final long durationUs;
-    public final int discontinuitySequenceNumber;
+    public final int relativeDiscontinuitySequence;
     public final long relativeStartTimeUs;
     public final boolean isEncrypted;
     public final String encryptionKeyUri;
@@ -43,12 +43,12 @@ public Segment(String uri, long byterangeOffset, long byterangeLength) {
       this(uri, 0, -1, C.TIME_UNSET, false, null, null, byterangeOffset, byterangeLength);
     }
 
-    public Segment(String uri, long durationUs, int discontinuitySequenceNumber,
+    public Segment(String uri, long durationUs, int relativeDiscontinuitySequence,
         long relativeStartTimeUs, boolean isEncrypted, String encryptionKeyUri, String encryptionIV,
         long byterangeOffset, long byterangeLength) {
       this.url = uri;
       this.durationUs = durationUs;
-      this.discontinuitySequenceNumber = discontinuitySequenceNumber;
+      this.relativeDiscontinuitySequence = relativeDiscontinuitySequence;
       this.relativeStartTimeUs = relativeStartTimeUs;
       this.isEncrypted = isEncrypted;
       this.encryptionKeyUri = encryptionKeyUri;
@@ -67,6 +67,8 @@ public int compareTo(Long relativeStartTimeUs) {
 
   public final long startOffsetUs;
   public final long startTimeUs;
+  public final boolean hasDiscontinuitySequence;
+  public final int discontinuitySequence;
   public final int mediaSequence;
   public final int version;
   public final long targetDurationUs;
@@ -76,11 +78,14 @@ public int compareTo(Long relativeStartTimeUs) {
   public final List<Segment> segments;
   public final long durationUs;
 
-  public HlsMediaPlaylist(String baseUri, long startOffsetUs, long startTimeUs, int mediaSequence,
-      int version, long targetDurationUs, boolean hasEndTag, boolean hasProgramDateTime,
+  public HlsMediaPlaylist(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) {
     super(baseUri, HlsPlaylist.TYPE_MEDIA);
     this.startTimeUs = startTimeUs;
+    this.hasDiscontinuitySequence = hasDiscontinuitySequence;
+    this.discontinuitySequence = discontinuitySequence;
     this.mediaSequence = mediaSequence;
     this.version = version;
     this.targetDurationUs = targetDurationUs;
@@ -123,19 +128,18 @@ public long getEndTimeUs() {
   }
 
   /**
-   * Returns a playlist identical to this one except for the start time, which is set to the
-   * specified value. If the start time already equals the specified value then the playlist will
-   * return itself.
+   * Returns a playlist identical to this one except for the start time, the discontinuity sequence
+   * and {@code hasDiscontinuitySequence} values. The first two are set to the specified values,
+   * {@code hasDiscontinuitySequence} is set to true.
    *
    * @param startTimeUs The start time for the returned playlist.
+   * @param discontinuitySequence The discontinuity sequence for the returned playlist.
    * @return The playlist.
    */
-  public HlsMediaPlaylist copyWithStartTimeUs(long startTimeUs) {
-    if (this.startTimeUs == startTimeUs) {
-      return this;
-    }
-    return new HlsMediaPlaylist(baseUri, startOffsetUs, startTimeUs, mediaSequence, version,
-        targetDurationUs, hasEndTag, hasProgramDateTime, initializationSegment, segments);
+  public HlsMediaPlaylist copyWith(long startTimeUs, int discontinuitySequence) {
+    return new HlsMediaPlaylist(baseUri, startOffsetUs, startTimeUs, true, discontinuitySequence,
+        mediaSequence, version, targetDurationUs, hasEndTag, hasProgramDateTime,
+        initializationSegment, segments);
   }
 
   /**
@@ -148,8 +152,9 @@ public HlsMediaPlaylist copyWithEndTag() {
     if (this.hasEndTag) {
       return this;
     }
-    return new HlsMediaPlaylist(baseUri, startOffsetUs, startTimeUs, mediaSequence, version,
-        targetDurationUs, true, hasProgramDateTime, initializationSegment, segments);
+    return new HlsMediaPlaylist(baseUri, startOffsetUs, startTimeUs, hasDiscontinuitySequence,
+        discontinuitySequence, mediaSequence, version, targetDurationUs, true, hasProgramDateTime,
+        initializationSegment, segments);
   }
 
 }

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

@@ -266,7 +266,9 @@ private static HlsMediaPlaylist parseMediaPlaylist(LineIterator iterator, String
     List<Segment> segments = new ArrayList<>();
 
     long segmentDurationUs = 0;
-    int discontinuitySequenceNumber = 0;
+    boolean hasDiscontinuitySequence = false;
+    int playlistDiscontinuitySequence = 0;
+    int relativeDiscontinuitySequence = 0;
     long playlistStartTimeUs = 0;
     long segmentStartTimeUs = 0;
     long segmentByteRangeOffset = 0;
@@ -323,9 +325,10 @@ private static HlsMediaPlaylist parseMediaPlaylist(LineIterator iterator, String
           segmentByteRangeOffset = Long.parseLong(splitByteRange[1]);
         }
       } else if (line.startsWith(TAG_DISCONTINUITY_SEQUENCE)) {
-        discontinuitySequenceNumber = Integer.parseInt(line.substring(line.indexOf(':') + 1));
+        hasDiscontinuitySequence = true;
+        playlistDiscontinuitySequence = Integer.parseInt(line.substring(line.indexOf(':') + 1));
       } else if (line.equals(TAG_DISCONTINUITY)) {
-        discontinuitySequenceNumber++;
+        relativeDiscontinuitySequence++;
       } else if (line.startsWith(TAG_PROGRAM_DATE_TIME)) {
         if (playlistStartTimeUs == 0) {
           long programDatetimeUs =
@@ -345,7 +348,7 @@ private static HlsMediaPlaylist parseMediaPlaylist(LineIterator iterator, String
         if (segmentByteRangeLength == C.LENGTH_UNSET) {
           segmentByteRangeOffset = 0;
         }
-        segments.add(new Segment(line, segmentDurationUs, discontinuitySequenceNumber,
+        segments.add(new Segment(line, segmentDurationUs, relativeDiscontinuitySequence,
             segmentStartTimeUs, isEncrypted, encryptionKeyUri, segmentEncryptionIV,
             segmentByteRangeOffset, segmentByteRangeLength));
         segmentStartTimeUs += segmentDurationUs;
@@ -358,7 +361,8 @@ private static HlsMediaPlaylist parseMediaPlaylist(LineIterator iterator, String
         hasEndTag = true;
       }
     }
-    return new HlsMediaPlaylist(baseUri, startOffsetUs, playlistStartTimeUs, mediaSequence, version,
+    return new HlsMediaPlaylist(baseUri, startOffsetUs, playlistStartTimeUs,
+        hasDiscontinuitySequence, playlistDiscontinuitySequence, mediaSequence, version,
         targetDurationUs, hasEndTag, playlistStartTimeUs != 0, initializationSegment, segments);
   }
 

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

@@ -334,47 +334,71 @@ private void notifyPlaylistBlacklisting(HlsUrl url, long blacklistMs) {
     }
   }
 
-  // TODO: Track discontinuities for media playlists that don't include the discontinuity number.
   private HlsMediaPlaylist getLatestPlaylistSnapshot(HlsMediaPlaylist oldPlaylist,
       HlsMediaPlaylist loadedPlaylist) {
-    if (loadedPlaylist.hasProgramDateTime) {
-      if (loadedPlaylist.isNewerThan(oldPlaylist)) {
-        return loadedPlaylist;
-      } else {
+    if (!loadedPlaylist.isNewerThan(oldPlaylist)) {
+      if (loadedPlaylist.hasEndTag) {
         // If the loaded playlist has an end tag but is not newer than the old playlist then we have
         // an inconsistent state. This is typically caused by the server incorrectly resetting the
         // media sequence when appending the end tag. We resolve this case as best we can by
         // returning the old playlist with the end tag appended.
-        return loadedPlaylist.hasEndTag ? oldPlaylist.copyWithEndTag() : oldPlaylist;
+        return oldPlaylist.copyWithEndTag();
+      } else {
+        return oldPlaylist;
       }
     }
-    // TODO: Once playlist type support is added, the snapshot's age can be added by using the
-    // target duration.
+    long startTimeUs = getLoadedPlaylistStartTimeUs(oldPlaylist, loadedPlaylist);
+    int discontinuitySequence = getLoadedPlaylistDiscontinuitySequence(oldPlaylist, loadedPlaylist);
+    return loadedPlaylist.copyWith(startTimeUs, discontinuitySequence);
+  }
+
+  private long getLoadedPlaylistStartTimeUs(HlsMediaPlaylist oldPlaylist,
+      HlsMediaPlaylist loadedPlaylist) {
+    if (loadedPlaylist.hasProgramDateTime) {
+      return loadedPlaylist.startTimeUs;
+    }
     long primarySnapshotStartTimeUs = primaryUrlSnapshot != null
         ? primaryUrlSnapshot.startTimeUs : 0;
     if (oldPlaylist == null) {
-      if (loadedPlaylist.startTimeUs == primarySnapshotStartTimeUs) {
-        // Playback has just started or is VOD so no adjustment is needed.
-        return loadedPlaylist;
-      } else {
-        return loadedPlaylist.copyWithStartTimeUs(primarySnapshotStartTimeUs);
-      }
+      return primarySnapshotStartTimeUs;
     }
-    if (!loadedPlaylist.isNewerThan(oldPlaylist)) {
-      // See comment above.
-      return loadedPlaylist.hasEndTag ? oldPlaylist.copyWithEndTag() : oldPlaylist;
+    int oldPlaylistSize = oldPlaylist.segments.size();
+    Segment firstOldOverlappingSegment = getFirstOldOverlappingSegment(oldPlaylist, loadedPlaylist);
+    if (firstOldOverlappingSegment != null) {
+      return oldPlaylist.startTimeUs + firstOldOverlappingSegment.relativeStartTimeUs;
+    } else if (oldPlaylistSize == loadedPlaylist.mediaSequence - oldPlaylist.mediaSequence) {
+      return oldPlaylist.getEndTimeUs();
+    } else {
+      // No segments overlap, we assume the new playlist start coincides with the primary playlist.
+      return primarySnapshotStartTimeUs;
     }
-    List<Segment> oldSegments = oldPlaylist.segments;
-    int oldPlaylistSize = oldSegments.size();
-    int mediaSequenceOffset = loadedPlaylist.mediaSequence - oldPlaylist.mediaSequence;
-    if (mediaSequenceOffset <= oldPlaylistSize) {
-      long adjustedNewPlaylistStartTimeUs = mediaSequenceOffset == oldPlaylistSize
-          ? oldPlaylist.getEndTimeUs()
-          : oldPlaylist.startTimeUs + oldSegments.get(mediaSequenceOffset).relativeStartTimeUs;
-      return loadedPlaylist.copyWithStartTimeUs(adjustedNewPlaylistStartTimeUs);
+  }
+
+  private int getLoadedPlaylistDiscontinuitySequence(HlsMediaPlaylist oldPlaylist,
+      HlsMediaPlaylist loadedPlaylist) {
+    if (loadedPlaylist.hasDiscontinuitySequence) {
+      return loadedPlaylist.discontinuitySequence;
+    }
+    // TODO: Improve cross-playlist discontinuity adjustment.
+    int primaryUrlDiscontinuitySequence = primaryUrlSnapshot != null
+        ? primaryUrlSnapshot.discontinuitySequence : 0;
+    if (oldPlaylist == null) {
+      return primaryUrlDiscontinuitySequence;
     }
-    // No segments overlap, we assume the new playlist start coincides with the primary playlist.
-    return loadedPlaylist.copyWithStartTimeUs(primarySnapshotStartTimeUs);
+    Segment firstOldOverlappingSegment = getFirstOldOverlappingSegment(oldPlaylist, loadedPlaylist);
+    if (firstOldOverlappingSegment != null) {
+      return oldPlaylist.discontinuitySequence
+          + firstOldOverlappingSegment.relativeDiscontinuitySequence
+          - loadedPlaylist.segments.get(0).relativeDiscontinuitySequence;
+    }
+    return primaryUrlDiscontinuitySequence;
+  }
+
+  private static Segment getFirstOldOverlappingSegment(HlsMediaPlaylist oldPlaylist,
+      HlsMediaPlaylist loadedPlaylist) {
+    int mediaSequenceOffset = loadedPlaylist.mediaSequence - oldPlaylist.mediaSequence;
+    List<Segment> oldSegments = oldPlaylist.segments;
+    return mediaSequenceOffset < oldSegments.size() ? oldSegments.get(mediaSequenceOffset) : null;
   }
 
   /**