Advance / delay only secondary (or only primary) subtitles

[Moschops]

I am using two different sets of subtitles, which is a fantastic capability of SMPlayer. Really helpful.

One set is bang on synchronised with what I'm watching. The other is a second or so out. Setting a subtitle delay (through Z and X keypresses) appears to affect both sets of subtitles; I'd really like it to only affect one set. Is that possible? I'd be happiest with a solution through SMplayer, but if there's only a solution working directly with MPlayer instead that too would be fine.

[rvm]

I think it's not possible. As far as I know mpv only has an option to set the subtitle delay.

https://mpv.io/manual/stable/#subtitles