fix(cea): Fix BUFFER_READ_OUT_OF_BOUNDS error when CEA caption packet…

…s are empty (shaka-project#3609)

Added check for empty caption packets in closed_caption_parser.

Added a unit test that verifies the closed_caption_parser now works with a video segment that contains empty caption packets.

Fixes shaka-project#3608

lib/media/closed_caption_parser.js

@@ -86,7 +86,9 @@ shaka.media.ClosedCaptionParser = class {
     for (const captionPacket of captionPackets) {
       const uint8ArrayData =
           shaka.util.BufferUtils.toUint8(captionPacket.packet);
-      this.ceaDecoder_.extract(uint8ArrayData, captionPacket.pts);
+      if (uint8ArrayData.length > 0) {
+        this.ceaDecoder_.extract(uint8ArrayData, captionPacket.pts);
+      }
     }
 
     // Decode and return the parsed captions.

test/media/closed_caption_parser_unit.js

@@ -0,0 +1,15 @@
+goog.require('shaka.media.ClosedCaptionParser');
+goog.require('shaka.test.Util');
+
+describe('ClosedCaptionParser', () => {
+  it('can handle empty caption packets', async () => {
+    const initSegment = await shaka.test.Util.fetch(
+        'base/test/test/assets/empty_caption_video_init.mp4');
+    const videoSegment = await shaka.test.Util.fetch(
+        'base/test/test/assets/empty_caption_video_segment.mp4');
+    const parser = new shaka.media.ClosedCaptionParser();
+    parser.init(initSegment);
+    parser.parseFrom(videoSegment);
+  });
+});
+