CC708 subtitle display issue with multiple windows in different priority

[fred0426]

I play a stream with CC708 subtitle on Exoplayer 2.13.1. The CC708 subtitle can NOT be displayed correctly with multiple windows that have different window priorities. Please see the below picture.

I found one line code is incorrect in Cea708Decoder class:

    Collections.sort(
        displayCueInfos,
        (thisInfo, thatInfo) -> Integer.compare(thisInfo.priority,thatInfo.priority));

should be changed to :

    Collections.sort(
        displayCueInfos,
        (thisInfo, thatInfo) -> Integer.compare(thatInfo.priority,thisInfo.priority));

So the sort is descending order, not ascending order. Thanks.

[icbaker]

Thanks for reporting this, I agree this is wrong, section 8.4.2 of the CEA-708B spec says (emphasis mine):

A higher priority (with 0 being the highest and 7 being the lowest) displayed window will overlap lower priority displayed windows on the screen.

I'll send a fix.

[icbaker]

Interestingly this also reveals an implicit assumption that the order of Cue objects passed to TextOutput.onCues indicates the order they should be drawn on the screen.

That should probably be more clearly documented on the TextOutput interface.