Use #EXT-X-START PRECISE attribute

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

@@ -597,20 +597,24 @@ public final class HlsMediaSource extends BaseMediaSource
     int segmentIndex = segments.size() - 1;
     long minStartPositionUs =
         playlist.durationUs + liveEdgeOffsetUs - C.msToUs(liveConfiguration.targetOffsetMs);
+    if (playlist.preciseStart)
+      return minStartPositionUs;
     while (segmentIndex > 0
         && segments.get(segmentIndex).relativeStartTimeUs > minStartPositionUs) {
       segmentIndex--;
     }
     HlsMediaPlaylist.Segment segment = segments.get(segmentIndex);
-    List<HlsMediaPlaylist.Part> parts = segment.parts;
-    int partIndex = parts.size();
-    if (partIndex > 1) {
-      HlsMediaPlaylist.Part part;
-      do {
-        partIndex--;
-        part = parts.get(partIndex);
-      } while (part.relativeStartTimeUs > minStartPositionUs || !part.isIndependent);
-      return part.relativeStartTimeUs;
+    if (playlist.startOffsetUs == C.TIME_UNSET) {
+      List<HlsMediaPlaylist.Part> parts = segment.parts;
+      int partIndex = parts.size();
+      if (partIndex > 1) {
+        HlsMediaPlaylist.Part part;
+        do {
+          partIndex--;
+          part = parts.get(partIndex);
+        } while (part.relativeStartTimeUs > minStartPositionUs || !part.isIndependent);
+        return part.relativeStartTimeUs;
+      }
     }
     return segment.relativeStartTimeUs;
   }

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

@@ -398,6 +398,10 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
    */
   public final long startOffsetUs;
   /**
+   * Whether the start position should be precise, as defined by #EXT-X-START.
+   */
+  public final boolean preciseStart;
+  /**
    * If {@link #hasProgramDateTime} is true, contains the datetime as microseconds since epoch.
    * Otherwise, contains the aggregated duration of removed segments up to this snapshot of the
    * playlist.
@@ -481,6 +485,7 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
       String baseUri,
       List<String> tags,
       long startOffsetUs,
+      boolean preciseStart,
       long startTimeUs,
       boolean hasDiscontinuitySequence,
       int discontinuitySequence,
@@ -499,6 +504,7 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
     super(baseUri, tags, hasIndependentSegments);
     this.playlistType = playlistType;
     this.startTimeUs = startTimeUs;
+    this.preciseStart = preciseStart;
     this.hasDiscontinuitySequence = hasDiscontinuitySequence;
     this.discontinuitySequence = discontinuitySequence;
     this.mediaSequence = mediaSequence;
@@ -576,6 +582,7 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
         baseUri,
         tags,
         startOffsetUs,
+        preciseStart,
         startTimeUs,
         /* hasDiscontinuitySequence= */ true,
         discontinuitySequence,
@@ -606,6 +613,7 @@ public final class HlsMediaPlaylist extends HlsPlaylist {
         baseUri,
         tags,
         startOffsetUs,
+        preciseStart,
         startTimeUs,
         hasDiscontinuitySequence,
         discontinuitySequence,

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

@@ -210,6 +210,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
   private static final Pattern REGEX_FORCED = compileBooleanAttrPattern("FORCED");
   private static final Pattern REGEX_INDEPENDENT = compileBooleanAttrPattern("INDEPENDENT");
   private static final Pattern REGEX_GAP = compileBooleanAttrPattern("GAP");
+  private static final Pattern REGEX_PRECISE = compileBooleanAttrPattern("PRECISE");
   private static final Pattern REGEX_VALUE = Pattern.compile("VALUE=\"(.+?)\"");
   private static final Pattern REGEX_IMPORT = Pattern.compile("IMPORT=\"(.+?)\"");
   private static final Pattern REGEX_VARIABLE_REFERENCE =
@@ -645,6 +646,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
     int relativeDiscontinuitySequence = 0;
     long playlistStartTimeUs = 0;
     long segmentStartTimeUs = 0;
+    boolean preciseStart = false;
     long segmentByteRangeOffset = 0;
     long segmentByteRangeLength = C.LENGTH_UNSET;
     long partStartTimeUs = 0;
@@ -687,6 +689,8 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
         isIFrameOnly = true;
       } else if (line.startsWith(TAG_START)) {
         startOffsetUs = (long) (parseDoubleAttr(line, REGEX_TIME_OFFSET) * C.MICROS_PER_SECOND);
+        preciseStart = parseOptionalBooleanAttribute(line, REGEX_PRECISE,
+                /* defaultValue= */ false);
       } else if (line.startsWith(TAG_SERVER_CONTROL)) {
         serverControl = parseServerControl(line);
       } else if (line.startsWith(TAG_PART_INF)) {
@@ -1011,6 +1015,7 @@ public final class HlsPlaylistParser implements ParsingLoadable.Parser<HlsPlayli
         baseUri,
         tags,
         startOffsetUs,
+        preciseStart,
         playlistStartTimeUs,
         hasDiscontinuitySequence,
         playlistDiscontinuitySequence,