Subtitle rendering intermittently stopping during playback on Smart TVs

[testeur-990]

Hello ,
We are facing an occasional issue where subtitles stop displaying while video playback is still running normally. The behavior appears to be random and so far has been difficult to reproduce.

What we know so far:

• The issue has been reported on Smart TV devices

• We currently don’t have any logs that capture the moment when it happens

• The reports are based mainly on end-user feedback

• Subtitles only reappear after a user interaction, such as seeking in the content

We wanted to check whether this is something you have already encountered, and if you might have any ideas or hypotheses about what could cause this kind of behavior.

Any insight would be greatly appreciated.

[kostalski]

Hi @testeur-990 ,
There can be multiple sources of such problem. For example:

• CSS issue on SmartTV app side (in case of rendering subtitles as HTML / custom rendered). Some older TV models got some own "CSS problems".
• Some old Samsung TV models MSE inconsistency
• Some small data inconsistency in subtitles timings and some older TV models can have problem with it (variant of MSE issue above).

More details will be helpful and are critical for reproducing issue:

1. What SmartTV platform (Samsung Tizen web app, LG WebOS app) ?
2. What version of SmartTV it was ? Maybe TV model is possible to get ? For Samsung TVs it is quite critical (Tizen 4.0 ~2018 year, was using WebKit WebView, in later versions Chromium WebView is used and this got impact on support, limitations & performance).
3. How subtitles are rendered (custom rendered or default from dash.js) ?
4. How subtitles are passed through (via external file, via DASH text track, what type of text track ttml/vtt) ?

[Murmur]

Maybe related to the following issues?

#4032
HbbTV-Association/ReferenceApplication#79

Test player with a fix, use NoDrm/1.4 Inband subtitles test case. Debug version is using the old DashJS_4.7.4 with a single line change. I have not tested a similar fix on DashjsV5 player yet.
https://refapp.hbbtv.org/staging/catalogue/index_mse-eme.php?dashjs=debug

function _handleHtmlCaption(currentItem, timeOffset, track) {
   ...
   //if (track.mode === _constants_Constants__WEBPACK_IMPORTED_MODULE_0__["default"].TEXT_SHOWING) {
   if (track.mode === "showing" || track.mode === "hidden") {
   ...
}