fix: re-open the MediaSource if readyState is not open when the init() method is called. (#7783)

Builds on top of @tykus160's observation in
#4903 where
`MediaSource.readyState` was either in a `closed` or `ended` state when
the `MediaSourceEngine.init()` logic is executed.

This fix will simply re-open the `MediaSource` if non-open, resulting in
fewer scenarios where the `MEDIA_SOURCE_OPERATION_THREW` error:
https://github.com/shaka-project/shaka-player/blob/de0f33c2623b057e80b7cafd53e19fac2f984961/lib/media/media_source_engine.js#L648-L651

is thrown because of an
[`InvalidStateError`](https://developer.mozilla.org/en-US/docs/Web/API/MediaSource/addSourceBuffer#exceptions).

Author: JulianDomingo

lib/media/media_source_engine.js

@@ -551,6 +551,13 @@ shaka.media.MediaSourceEngine = class {
     const ContentType = shaka.util.ManifestParserUtils.ContentType;
 
     await this.mediaSourceOpen_;
+    if (this.ended() || this.closed()) {
+      shaka.log.alwaysError('Expected MediaSource to be open during init(); ' +
+          'reopening the media source.');
+      this.mediaSourceOpen_ = new shaka.util.PublicPromise();
+      this.mediaSource_ = this.createMediaSource(this.mediaSourceOpen_);
+      await this.mediaSourceOpen_;
+    }
 
     this.sequenceMode_ = sequenceMode;
     this.manifestType_ = manifestType;
@@ -724,6 +731,17 @@ shaka.media.MediaSourceEngine = class {
     return this.mediaSource_ ? this.mediaSource_.readyState == 'ended' : true;
   }
 
+  /**
+   * @return {boolean} True if the MediaSource is in an "closed" state, or if
+   *   the object has been destroyed.
+   */
+  closed() {
+    if (this.reloadingMediaSource_) {
+      return false;
+    }
+    return this.mediaSource_ ? this.mediaSource_.readyState == 'closed' : true;
+  }
+
   /**
    * Gets the first timestamp in buffer for the given content type.
    *
@@ -1608,7 +1626,7 @@ shaka.media.MediaSourceEngine = class {
       // don't call it again. Also do not call if readyState is
       // 'closed' (not attached to video element) since it is not a
       // valid operation.
-      if (this.ended() || this.mediaSource_.readyState === 'closed') {
+      if (this.ended() || this.closed()) {
         return;
       }
       // Tizen won't let us pass undefined, but it will let us omit the

test/media/media_source_engine_unit.js

@@ -165,6 +165,10 @@ describe('MediaSourceEngine', () => {
     videoSourceBuffer = createMockSourceBuffer();
     mockMediaSource = createMockMediaSource();
     mockMediaSource.addSourceBuffer.and.callFake((mimeType) => {
+      if (mockMediaSource.readyState !== 'open') {
+        // https://w3c.github.io/media-source/#addsourcebuffer-method
+        throw new Error('InvalidStateError');
+      }
       const type = mimeType.split('/')[0];
       const buffer = type == 'audio' ? audioSourceBuffer : videoSourceBuffer;
 
@@ -200,6 +204,7 @@ describe('MediaSourceEngine', () => {
     createMediaSourceSpy = jasmine.createSpy('createMediaSource');
     createMediaSourceSpy.and.callFake((p) => {
       p.resolve();
+      mockMediaSource.readyState = 'open';
       return mockMediaSource;
     });
     // eslint-disable-next-line no-restricted-syntax
@@ -400,6 +405,32 @@ describe('MediaSourceEngine', () => {
       expect(shaka.text.TextEngine).not.toHaveBeenCalled();
     });
 
+    it('creates SourceBuffers when MediaSource readyState is closed',
+        async () => {
+          const initObject = new Map();
+          initObject.set(ContentType.AUDIO, fakeAudioStream);
+          initObject.set(ContentType.VIDEO, fakeVideoStream);
+
+          await mediaSourceEngine.open();
+
+          mockMediaSource.readyState = 'closed';
+          await expectAsync(
+              mediaSourceEngine.init(initObject, false)).not.toBeRejected();
+        });
+
+    it('creates SourceBuffers when MediaSource readyState is ended',
+        async () => {
+          const initObject = new Map();
+          initObject.set(ContentType.AUDIO, fakeAudioStream);
+          initObject.set(ContentType.VIDEO, fakeVideoStream);
+
+          await mediaSourceEngine.open();
+
+          mockMediaSource.readyState = 'ended';
+          await expectAsync(
+              mediaSourceEngine.init(initObject, false)).not.toBeRejected();
+        });
+
     it('creates TextEngines for text types', async () => {
       const initObject = new Map();
       initObject.set(ContentType.TEXT, fakeTextStream);