fix: Pass correct adaptation value to MediaSourceEngine (#7111)

Currently passing adaptation value via media state has 2 flaws:
- it's not passed on init segment append (thus we don't use this value
at all in CaptionParser)
- it often marks already pending update as an adaptation, instead of the
actual segment we care about

lib/media/streaming_engine.js

@@ -1348,6 +1348,8 @@ shaka.media.StreamingEngine = class {
       return this.config_.updateIntervalSeconds / 2;
     }
 
+    // Lack of segment iterator is the best indicator stream has changed.
+    const streamChanged = !mediaState.segmentIterator;
     const reference = this.getSegmentReferenceNeeded_(
         mediaState, presentationTime, bufferEnd);
     if (!reference) {
@@ -1357,6 +1359,14 @@ shaka.media.StreamingEngine = class {
       // a SegmentReference eventually.
       return this.config_.updateIntervalSeconds;
     }
+    // Get media state adaptation and reset this value. By guarding it during
+    // actual stream change we ensure it won't be cleaned by accident on regular
+    // append.
+    let adaptation = false;
+    if (streamChanged && mediaState.adaptation) {
+      adaptation = true;
+      mediaState.adaptation = false;
+    }
 
     // Do not let any one stream get far ahead of any other.
     let minTimeNeeded = Infinity;
@@ -1395,7 +1405,8 @@ shaka.media.StreamingEngine = class {
       mediaState.segmentPrefetch.prefetchSegmentsByTime(reference.startTime);
     }
 
-    const p = this.fetchAndAppend_(mediaState, presentationTime, reference);
+    const p = this.fetchAndAppend_(mediaState, presentationTime, reference,
+        adaptation);
     p.catch(() => {});  // TODO(#1993): Handle asynchronous errors.
     return null;
   }
@@ -1517,9 +1528,10 @@ shaka.media.StreamingEngine = class {
    * @param {!shaka.media.StreamingEngine.MediaState_} mediaState
    * @param {number} presentationTime
    * @param {!shaka.media.SegmentReference} reference
+   * @param {boolean} adaptation
    * @private
    */
-  async fetchAndAppend_(mediaState, presentationTime, reference) {
+  async fetchAndAppend_(mediaState, presentationTime, reference, adaptation) {
     const ContentType = shaka.util.ManifestParserUtils.ContentType;
     const StreamingEngine = shaka.media.StreamingEngine;
     const logPrefix = StreamingEngine.logPrefix_(mediaState);
@@ -1548,7 +1560,7 @@ shaka.media.StreamingEngine = class {
             shaka.util.Error.Category.NETWORK,
             shaka.util.Error.Code.SEGMENT_MISSING);
       }
-      await this.initSourceBuffer_(mediaState, reference);
+      await this.initSourceBuffer_(mediaState, reference, adaptation);
       this.destroyer_.ensureNotDestroyed();
       if (this.fatalError_) {
         return;
@@ -1605,7 +1617,7 @@ shaka.media.StreamingEngine = class {
               remaining = remaining.subarray(offset);
               await this.append_(
                   mediaState, presentationTime, stream, reference, dataToAppend,
-                  /* isChunkedData= */ true);
+                  /* isChunkedData= */ true, adaptation);
 
               if (mediaState.segmentPrefetch && mediaState.segmentIterator) {
                 mediaState.segmentPrefetch.prefetchSegmentsByTime(
@@ -1644,8 +1656,8 @@ shaka.media.StreamingEngine = class {
             return;
           }
 
-          await this.append_(
-              mediaState, presentationTime, stream, reference, result);
+          await this.append_(mediaState, presentationTime, stream, reference,
+              result, /* chunkedData= */ false, adaptation);
         }
 
         if (mediaState.segmentPrefetch && mediaState.segmentIterator) {
@@ -1676,8 +1688,8 @@ shaka.media.StreamingEngine = class {
           return;
         }
 
-        await this.append_(
-            mediaState, presentationTime, stream, reference, result);
+        await this.append_(mediaState, presentationTime, stream, reference,
+            result, /* chunkedData= */ false, adaptation);
       }
 
       this.destroyer_.ensureNotDestroyed();
@@ -1876,10 +1888,11 @@ shaka.media.StreamingEngine = class {
    *
    * @param {shaka.media.StreamingEngine.MediaState_} mediaState
    * @param {!shaka.media.SegmentReference} reference
+   * @param {boolean} adaptation
    * @return {!Promise}
    * @private
    */
-  async initSourceBuffer_(mediaState, reference) {
+  async initSourceBuffer_(mediaState, reference, adaptation) {
     const ContentType = shaka.util.ManifestParserUtils.ContentType;
     const MimeUtils = shaka.util.MimeUtils;
     const StreamingEngine = shaka.media.StreamingEngine;
@@ -2039,7 +2052,8 @@ shaka.media.StreamingEngine = class {
                 mediaState.type, initSegment);
             await this.playerInterface_.mediaSourceEngine.appendBuffer(
                 mediaState.type, initSegment, /* reference= */ null,
-                mediaState.stream, hasClosedCaptions);
+                mediaState.stream, hasClosedCaptions, mediaState.seeked,
+                adaptation);
           } catch (error) {
             mediaState.lastInitSegmentReference = null;
             throw error;
@@ -2133,11 +2147,12 @@ shaka.media.StreamingEngine = class {
    * @param {!shaka.media.SegmentReference} reference
    * @param {BufferSource} segment
    * @param {boolean=} isChunkedData
+   * @param {boolean=} adaptation
    * @return {!Promise}
    * @private
    */
   async append_(mediaState, presentationTime, stream, reference, segment,
-      isChunkedData = false) {
+      isChunkedData = false, adaptation = false) {
     const logPrefix = shaka.media.StreamingEngine.logPrefix_(mediaState);
 
     const hasClosedCaptions = stream.closedCaptions &&
@@ -2230,8 +2245,6 @@ shaka.media.StreamingEngine = class {
     // appendBuffer() call.
     const seeked = mediaState.seeked;
     mediaState.seeked = false;
-    const adaptation = mediaState.adaptation;
-    mediaState.adaptation = false;
 
     await this.playerInterface_.beforeAppendSegment(mediaState.type, segment);
     await this.playerInterface_.mediaSourceEngine.appendBuffer(