Support for Rollup Captions

[damascene]

I would like to ask if possible to support Rollup captions as used in Youtube. It seems like the subtitle is rolling up instead of flashing on screen.

It works best with machine generated text where there could be not very accurate separation between sentences so the software will show the previous subtitle on one line and the current one in another line and people can link them in their brain.

Here is an example on how the subtitle file is generated by Youtube, notice the line reputation :

00:00 --> 00:03 
This is the first line

00:03 --> 00:10 
This is the first line
This is what happens when another line is added

00:10
This is what happens when another line is added
If a third one is added, the first one disappears and the second one shoots up

More info about roll-up captions at this link: https://www.w3.org/community/texttracks/wiki/RollupCaptions

One person wants to convert the rolling subtitle to normal one, but maybe if good support for rolling subtitle is implemented it could be used:

https://github.com/yt-dlp/yt-dlp/issues/1734

I wonder if it's possible to get support for rolling subtitle in the software. I suggest to change the color of the previous line to a different color than the current line to give better feeling as it could be confusing sometimes.