fix: Handle ID3 EMSG duration according to AOM spec (#9757)

Fixes https://github.com/shaka-project/shaka-player/issues/9753

lib/media/media_source_engine.js

@@ -1042,7 +1042,13 @@ shaka.media.MediaSourceEngine = class {
       } else {
         // All other schemes are dispatched as a general 'emsg' event.
 
-        const endTime = startTime + (eventDuration / timescale);
+        let endTime = startTime;
+        // See: https://aomediacodec.github.io/id3-emsg/
+        // ID3 EMSG events do not carry a duration
+        if (schemeId !== 'https://aomedia.org/emsg/ID3' ||
+            eventDuration !== 0xFFFFFFFF) {
+          endTime += eventDuration / timescale;
+        }
         /** @type {shaka.extern.EmsgInfo} */
         const emsg = {
           startTime: startTime,

test/media/media_source_engine_integration.js

@@ -801,6 +801,35 @@ describe('MediaSourceEngine', () => {
       '53 68 61 6b  61 33 44 49   03 00 40 00  00 00 1b'
     ).replace(/\s/g, ''));
 
+    const emsgSegmentV0ID3WithoutDuration = Uint8ArrayUtils.fromHex((
+      // 105 bytes  emsg box     v0, flags 0
+      '00 00 00 69  65 6d 73 67  00 00 00 00' +
+
+      // scheme id uri (13 bytes) 'https://aomedia.org/emsg/ID3'
+      '68 74 74 70  73 3a 2f 2f   61 6f 6d 65  64 69 61 2e' +
+      '6f 72 67 2f  65 6d 73 67   2f 49 44 33  00' +
+
+      // value (1 byte) ''
+      '00' +
+
+      // timescale (4 bytes) 1
+      '00 00 00 01' +
+
+      // presentation time delta (4 bytes) 8
+      '00 00 00 08' +
+
+      // event duration (4 bytes) 255
+      'ff ff ff ff' +
+
+      // id (4 bytes) 51
+      '00 00 00 33' +
+
+      // message data (47 bytes)
+      '49 44 33 03  00 40 00 00   00 1b 00 00  00 06 00 00' +
+      '00 00 00 02  54 58 58 58   00 00 00 07  e0 00 03 00' +
+      '53 68 61 6b  61 33 44 49   03 00 40 00  00 00 1b'
+    ).replace(/\s/g, ''));
+
     const id3SchemeUri = 'https://aomedia.org/emsg/ID3';
 
     const emsgObj = {
@@ -839,6 +868,18 @@ describe('MediaSourceEngine', () => {
       messageData: new Uint8Array([0x74, 0x65, 0x73, 0x74]),
     };
 
+    const emsgObjSegmentV0ID3WithoutDuration = {
+      startTime: 8,
+      endTime: 8,
+      schemeIdUri: 'https://aomedia.org/emsg/ID3',
+      value: '',
+      timescale: 1,
+      presentationTimeDelta: 8,
+      eventDuration: 4294967295,
+      id: 51,
+      messageData: jasmine.any(Uint8Array),
+    };
+
     const initSegmentReference = new shaka.media.InitSegmentReference(
         /* uris= */ () => [],
         /* startByte= */ 0,
@@ -989,6 +1030,29 @@ describe('MediaSourceEngine', () => {
       expect(onMetadata).toHaveBeenCalled();
     });
 
+    // eslint-disable-next-line @stylistic/max-len
+    it('triggers both emsg event and metadata event for ID3 without duration', () => {
+      const videoStream =
+          shaka.test.StreamingEngineUtil.createMockVideoStream(1);
+      videoStream.emsgSchemeIdUris = [id3SchemeUri];
+
+      onEvent.and.callFake((emsgEvent) => {
+        expect(emsgEvent.type).toBe('emsg');
+      });
+
+      mediaSourceEngine.getTimestampAndDispatchMetadata(
+          ContentType.VIDEO,
+          emsgSegmentV0ID3WithoutDuration,
+          reference,
+          videoStream,
+          /* mimeType= */ 'video/mp4');
+
+      expect(onEmsg).toHaveBeenCalledTimes(1);
+      const emsgInfo = onEmsg.calls.argsFor(0)[0];
+      expect(emsgInfo).toEqual(emsgObjSegmentV0ID3WithoutDuration);
+      expect(onMetadata).toHaveBeenCalled();
+    });
+
     it('event start matches presentation time', () => {
       const videoStream =
           shaka.test.StreamingEngineUtil.createMockVideoStream(1);