High memory usage when loading external subtitles in LEGACY mode

[Mountains-0]

When I use the LEGACY mode to load external ASS subtitles, I found that the AssSubtitleParser.parse method renders all subtitles into bitmaps at once. This causes high memory usage and eventually leads to an OOM error, even with a regular 1080P video.
Here is the link to the subtitle file: https://github.com/Mountains-0/test_subtitle/blob/main/Interstellar.ass

[peerless2012]

I have no time to see this issue, and try the new OVERLAY mode, it's friendly for external subtitles.