fix(StreamingEngine): clear lastInitSegmentReference when clearing bu…

…ffer

When toggling between two text streams quickly(for example en -> fr ->
en), the mediaState's lastInitSegmentReference may not get updated to
'fr' before switching back to 'en'. That way, in initSourceBuffer_(),
the initSegmentReference is considered as fetched and appended, but the
buffer was in fact cleared.

Setting lastInitSegmentReference to null every time we clear the
buffer, and fetch and append the initSegmentReference with the new
update.

b/168253400

Change-Id: Id6378bdadd34f93a2a2f54ac84d82cf39b89716e

lib/media/streaming_engine.js

@@ -1734,6 +1734,7 @@ shaka.media.StreamingEngine = class {
     mediaState.clearBufferSafeMargin = 0;
     mediaState.clearingBuffer = true;
     mediaState.lastSegmentReference = null;
+    mediaState.lastInitSegmentReference = null;
     mediaState.segmentIterator = null;
 
     shaka.log.debug(logPrefix, 'clearing buffer');

test/media/streaming_engine_unit.js

@@ -897,9 +897,11 @@ describe('StreamingEngine', () => {
           });
         });
         manifest.addTextStream(20, (stream) => {
+          stream.setInitSegmentReference(['text-20-init'], 0, null);
           stream.useSegmentTemplate('text-20-%d.mp4', 10);
         });
         manifest.addTextStream(21, (stream) => {
+          stream.setInitSegmentReference(['text-21-init'], 0, null);
           stream.useSegmentTemplate('text-21-%d.mp4', 10);
         });
       });
@@ -987,10 +989,9 @@ describe('StreamingEngine', () => {
     });
 
     // See https://github.com/google/shaka-player/issues/2956
-    it('works with fast stream switches during update', async () => {
+    it('works with fast variant switches during update', async () => {
       // Delay the appendBuffer call until later so we are waiting for this to
       // finish when we switch.
-      const Util = shaka.test.Util;
       const p = new shaka.util.PublicPromise();
       const old = mediaSourceEngine.appendBuffer;
       // Replace the whole spy since we want to call the original.
@@ -1013,6 +1014,39 @@ describe('StreamingEngine', () => {
 
       expect(Util.invokeSpy(mediaSourceEngine.bufferEnd, 'video')).toBe(10);
     });
+
+    it('works with fast text stream switches during update', async () => {
+      // Delay the appendBuffer call until later so we are waiting for this to
+      // finish when we switch.
+      const p = new shaka.util.PublicPromise();
+
+      const old = mediaSourceEngine.appendBuffer;
+      // Replace the whole spy since we want to call the original.
+      mediaSourceEngine.appendBuffer =
+          jasmine.createSpy('appendBuffer')
+              .and.callFake(async (type, data, start, end) => {
+                await p;
+                return Util.invokeSpy(old, type, data, start, end);
+              });
+
+      await streamingEngine.start();
+      playing = true;
+
+      await Util.fakeEventLoop(3);
+      netEngine.request.calls.reset();
+
+      streamingEngine.switchTextStream(newTextStream);
+      streamingEngine.switchTextStream(initialTextStream);
+      p.resolve();
+
+      await Util.fakeEventLoop(5);
+
+      const segmentType = shaka.net.NetworkingEngine.RequestType.SEGMENT;
+      // Quickly switching back to text1, and text init segment should be
+      // fetched again.
+      netEngine.expectRequest('text-20-init', segmentType);
+      netEngine.expectNoRequest('text-21-init', segmentType);
+    });
   });
 
   describe('handles seeks (VOD)', () => {