VOD content Embedded Captions Flashing-in and out issue.

[ajayhack]

Version

Media3 1.10.1

More version details

We are currently using Media3 version 1.10.1 in our codebase. When playing VOD content with embedded captions, we are seeing an issue where the captions continuously flash in and out. They appear for a few milliseconds and then disappear, repeating throughout the entire stream.

we will share stream url on email.

Devices that reproduce the issue

Samsung Galaxy A62 and other android devices too.

Devices that do not reproduce the issue

NA

Reproducible in the demo app?

Yes

Reproduction steps

Play shared stream on email with Media 3 Demo app where trackselection code is there then on showing cc you will observe the flashing-in and out captions issue.

Expected result

Embedded Captions should show properly without flashing-in and out issue.

Actual result

Embedded Captions flashing-in and out issue.

Media

Stream URL sharing on email.

Bug Report

• You will email the zip file produced by adb bugreport to android-media-github@google.com after filing this issue.

[microkatz]

Hi!

Thank you for reporting your issue!

First, I checked your attached bug report and did not find any exoplayer logs/traces. If you could please reproduce the issue with the demo app and create a bug report as per these instructions then that would be great!

Also I tried to stream the url you sent in the same email but got a 403 response error. Is the content accessible? Is it regionally tied? If you could please double check and send us a new link.

If you are unable to share the bug report or test content publicly, please send them to android-media-github@google.com with the subject Issue #3384. Please also update this issue to indicate you've done this. Thanks!

[ajayhack]

Hello @microkatz
Shared the latest stream URL via email with android-media-github@google.com. Please check it once. I have also shared the Media3 Demo App bug report attachment.

Just paste stream url in Media 3 Demo repo and enable "CC" from player options.
Please check stream asap , As every stream has some expiry timeout based on token.

[microkatz]

Hi @ajayhack

EDIT: See following comment:

Thank you for providing the sample stream and bug report! I was able to reproduce your issue.

Root Cause

• Sequence Number Discontinuities: The CEA-708 DTVCC packets include a 2-bit rolling sequence counter (0..3). In your stream, the encoder did not maintain a continuous rolling sequence counter across periods of silence or segment boundaries.
• Aggressive Reset in Cea708Decoder: When encountering a non-sequential packet number, ExoPlayer's Cea708Decoder was treating the discontinuity as a fatal stream error and resetting all active window builders (resetCueBuilders()). Because each caption fragment arrived and was immediately followed by a sequence discontinuity, the decoder wiped out the active caption window ~33ms after displaying it, causing the rapid flashing in and out.

EDIT: Per the CTA-708 specification, a transport-level sequence number discontinuity indicates potential packet loss and should discard partially accumulated packets as well as perform a RESET command.

I'm reviewing a potential fix and will update this ticket when the issue has been addressed!

[microkatz]

Hello @ajayhack,

Update:

In our review of the Cea 708 spec, it reads as follows:

Section 5:

When a lost packet is detected, any partially accumulated data from the previously received packet is to be discarded, and the processing associated with the Reset command should be performed for each existing service. See section 8.9.5.

And 8.9.5 says:

The 'resetting' or 're-initialization' of service means:

• that the service's windows are removed from the display
• all defined windows for the service are deleted
• all window and pen attributes for the service are deleted, and
  the Service Input Buffer is cleared.

So it is by spec that ExoPlayer is removing the captions on the screen.

Is there any chance that you can fix your content to correct the sequence numbers?

[ajayhack]

@microkatz
The stream is from a third party. Is there any workaround available in Media3 that could help fix this issue on the player side?