fix: Add support to crossBoundaryStrategy when using HLS (#8343)

Related to #8335

Author: avelad

lib/hls/hls_parser.js

@@ -4277,6 +4277,10 @@ shaka.hls.HlsParser = class {
           item.tags, 'EXT-X-DISCONTINUITY');
       if (discontinuityTag) {
         discontinuitySequence++;
+
+        if (previousReference && previousReference.initSegmentReference) {
+          previousReference.initSegmentReference.boundaryEnd = startTime;
+        }
       }
 
       // Apply new AES tags as you see them, keeping a running total.

lib/media/streaming_engine.js

@@ -3045,17 +3045,26 @@ shaka.media.StreamingEngine = class {
     const mediaState = this.mediaStates_.get(ContentType.VIDEO) ||
       this.mediaStates_.get(ContentType.AUDIO);
 
-    if (!mediaState || !mediaState.lastAppendWindowEnd ||
-        mediaState.clearingBuffer) {
+    if (!mediaState || mediaState.clearingBuffer) {
       return;
     }
 
+    const lastInitRef = mediaState.lastInitSegmentReference;
+    if (!lastInitRef) {
+      return;
+    }
+
+    const boundaryEnd = lastInitRef.boundaryEnd;
+    if (boundaryEnd == null) {
+      return;
+    }
     const threshold = shaka.media.StreamingEngine.CROSS_BOUNDARY_END_THRESHOLD_;
-    const fromEnd = mediaState.lastAppendWindowEnd - presentationTime;
+    const fromEnd = boundaryEnd - presentationTime;
     // Check if greater than 0 to eliminate a backwards seek.
     if (fromEnd > 0 && fromEnd < threshold) {
       // Set the intended time to seek to in order to cross the boundary.
-      this.boundaryTime_ = mediaState.lastAppendWindowEnd;
+      this.boundaryTime_ = boundaryEnd +
+          shaka.media.StreamingEngine.APPEND_WINDOW_END_FUDGE_;
 
       if (immediate) {
         this.crossBoundaryTimer_.tickNow();