clear buffer on unbuffered seek for updating media states

lib/media/streaming_engine.js

@@ -628,7 +628,7 @@ shaka.media.StreamingEngine = class {
 
         // Don't clear the buffer unless something is buffered.  This extra
         // check prevents extra, useless calls to clear the buffer.
-        if (somethingBuffered) {
+        if (somethingBuffered || mediaState.performingUpdate) {
           this.forceClearBuffer_(mediaState);
           streamCleared = true;
         }

test/media/streaming_engine_unit.js

@@ -97,6 +97,9 @@ describe('StreamingEngine', () => {
   /** @type {!shaka.media.StreamingEngine} */
   let streamingEngine;
 
+  /** @type {function(function(), number)} */
+  let realSetTimeout;
+
   /**
    * Runs the fake event loop.
    * @param {function()=} callback An optional callback that is executed
@@ -116,6 +119,7 @@ describe('StreamingEngine', () => {
   }
 
   beforeAll(() => {
+    realSetTimeout = window.setTimeout;
     jasmine.clock().install();
     jasmine.clock().mockDate();
   });
@@ -1391,6 +1395,66 @@ describe('StreamingEngine', () => {
       });
     });
 
+    it('into unbuffered regions when nothing is buffered ' +
+      'and mediaState is performing an update', async () => {
+      // Here we go!
+      streamingEngine.switchVariant(variant);
+      streamingEngine.switchTextStream(textStream);
+      // ensure init source buffer promise does not resolve before seeked()
+      // so mediaState remains in "performingUpdate" state
+      const initSourceBufferPromise = new shaka.util.PublicPromise();
+      mediaSourceEngine.setStreamProperties.and
+          .returnValue(initSourceBufferPromise);
+      await streamingEngine.start();
+      playing = true;
+
+      // tick to trigger mediaState updates
+      jasmine.clock().tick(1);
+      // give a chance for fetchAndAppend_ to be invoked
+      // by async onUpdate_ callback
+      await Util.shortDelay(realSetTimeout);
+
+      // Nothing is buffered yet.
+      expect(mediaSourceEngine.segments).toEqual({
+        audio: [false, false, false, false],
+        video: [false, false, false, false],
+        text: [false, false, false, false],
+      });
+
+      // Seek forward to an unbuffered region in the first Period.
+      presentationTimeInSeconds = 15;
+      streamingEngine.seeked();
+
+      // resolve initSourceBufferPromise after seeked(), waitingToClearBuffer
+      // should have been set, so this will now trigger the actual flush of
+      // the buffer
+      initSourceBufferPromise.resolve();
+      mediaSourceEngine.setStreamProperties.and
+          .returnValue(Promise.resolve());
+
+      // allow mediaState update to resolve
+      await Util.shortDelay(realSetTimeout);
+
+      onTick.and.callFake(() => {
+        expect(mediaSourceEngine.clear).toHaveBeenCalled();
+        onTick.and.stub();
+      });
+
+      await runTest(Util.spyFunc(onTick));
+
+      // Verify buffers.
+      expect(mediaSourceEngine.initSegments).toEqual({
+        audio: [false, true],
+        video: [false, true],
+        text: [],
+      });
+      expect(mediaSourceEngine.segments).toEqual({
+        audio: [false, true, true, true],
+        video: [false, true, true, true],
+        text: [false, true, true, true],
+      });
+    });
+
     it('into unbuffered regions near segment start', async () => {
       // Here we go!
       streamingEngine.switchVariant(variant);