Comment by akiselev

I think that point should be amended to say "rendering subtitles at the output resolution is always better than rendering them at the video resolution." You don't want to upscale 244p soft subtitles to 1080p but you do want to default to giving video authors creative control over how the subtitles are displayed. The ASS subtitle format allows for some very complex styling that can be used as an artistic element in video (or just to make sure there's proper contrast, can be read by color blind people, character differentiation, etc.) so you generally don't want to assume anything. There's also the issue of coordinates for where the subtitles are supposed to be that all go to shit if you render them on a transformed (up/downscaled) frame.