fix: Adjust timing of mediaqualitychanged event when safe margin is s…

…et (#7114)

lib/media/streaming_engine.js

@@ -1958,6 +1958,8 @@ shaka.media.StreamingEngine = class {
     const MimeUtils = shaka.util.MimeUtils;
     const StreamingEngine = shaka.media.StreamingEngine;
     const logPrefix = StreamingEngine.logPrefix_(mediaState);
+    const nullLastReferences = mediaState.lastSegmentReference == null &&
+      mediaState.lastInitSegmentReference == null;
 
     /** @type {!Array.<!Promise>} */
     const operations = [];
@@ -2120,8 +2122,19 @@ shaka.media.StreamingEngine = class {
             throw error;
           }
         };
+        let initSegmentTime = reference.startTime;
+        if (nullLastReferences) {
+          const bufferEnd =
+            this.playerInterface_.mediaSourceEngine.bufferEnd(mediaState.type);
+          if (bufferEnd != null) {
+            // Adjust init segment appendance time if we have something in
+            // a buffer, i.e. due to running switchVariant() with non zero
+            // safe margin value.
+            initSegmentTime = bufferEnd;
+          }
+        }
         this.playerInterface_.onInitSegmentAppended(
-            reference.startTime, reference.initSegmentReference);
+            initSegmentTime, reference.initSegmentReference);
         operations.push(append());
       }
     }